Since the Cold War ended two decades ago, Washington has considered Moscow mostly as an unreliable ally — and, at times, a stubborn adversary, in efforts to boost the global economy, curb weapons proliferation and calm other nations in tumult. At the same time, Russia’s role as a key participant in international efforts to solve global crises gives it the ability to hurt the U.S. if it decides to be uncooperative or openly obstructive.

Some of the tensions can be chalked up to pure competition. The range and scope of Russia’s natural resources are second only to the U.S. and it is the world’s largest natural-gas exporter. Moscow has stepped up diplomatic ties with China and, more recently, across the Mideast to provide a counterpoint to Western influences in countries the U.S. is trying to win over. This week, President Barack Obama downplayed Russia as a “regional power” — despite Russian President Vladimir Putin’s clear desire to restore his country to the global superpower status it held as the core of the Soviet Union.

The monthlong crisis in Ukraine that led to Russia annexing the strategic Crimean Peninsula has forged a new bitterness between Moscow and Washington. It’s too soon to say whether relations will fully freeze over, especially in areas where both sides share a common interest. But, “given Putin shows no signs of backing down here,” former Obama administration national security adviser Tom Donilon said earlier this month, “I think we’re in for a very difficult time in Russia-U.S. relations.”

Some key areas where the U.S. and Russia are still working together — for now.

IRAN

Both Russia and the U.S. have been clear about wanting to limit Iran’s ability to build a nuclear bomb. At last week’s negotiations session in Vienna between world powers and Iran, officials said U.S. and Russian diplomats openly agreed to ignore other topics and together focus on the talks with Tehran.

Iran often sought to exploit U.S.-Russian differences in the past and it may use the current tensions to resist significant nuclear cutbacks. Moscow already has an agreeable relationship with Tehran: Russia is one of Iran’s main trading partners and has sold Iran arms over the years. Russia built Iran’s first nuclear reactor and is drafting an agreement to build two more.

Russian Deputy Foreign Minister Sergei Ryabkov warned last week that Moscow wouldn’t like to use the negotiations with Iran as “an element of the game of raising the stakes” with the West amid tensions over Ukraine. But he added that, “if they force us into that, we will take retaliatory measures.”

However, the U.S. has developed much of the negotiation strategy against Iran. Harsh U.S. and European Union sanctions against oil exports and threat of U.S. or Israeli military action has, says former U.S. Ambassador James F. Jeffrey, largely been the driving force behind Iran’s willingness to negotiate. “These tools remain with or without Russian cooperation,” says Jeffrey, a fellow at the Washington Institute for Near East Policy.

SYRIA

Russia and the U.S. have been at odds over Syria, where Washington and the West want to see opposition forces succeed in their three-year battle against Syrian President Bashar Assad, who has Moscow’s support. Russia has sold weapons to Syria’s military and repeatedly blocked United Nations resolutions to condemn or sanction Assad’s government. If Russia chooses to play a spoiler on Syria, it may boost financial aid and weapons supplies to Assad.

However, Russia has agreed to help broker a cease-fire and a transitional government, and over the last year has worked with the U.S. to bring Assad officials and rebel leaders to negotiate. But those efforts have failed to yield any breakthroughs. Russia is also vital in leaning on Assad’s government to give up its chemical weapons stockpile — less than half of which has been shipped out against a June 30 deadline.

“It’s not that we need something from Russia — it’s that the Syrian people need the Russians and the Iranians and anyone else with influence over the regime to keep pushing them,” State Department deputy spokeswoman Marie Harf said Wednesday. “Quite frankly, we have been able to work together on Syria, on things like chemical weapons, even when we very strongly disagree with other parts of their Syria policy, certainly.”

AFGHANISTAN

Russia has played a key role in providing air and land corridors for supplying the U.S. and other coalition troops in Afghanistan. It has provided an alternative to a route through Pakistan, which has been unstable amid local protests.

If Russia chooses to shut the transit route, it would swell U.S. costs and may cause major logistical challenges as the U.S. and its allies pull their forces out of Afghanistan this year.

Putin appeared to signal last week that Russia wants to continue to cooperate on Afghanistan. He said that Russia will keep funding a program run jointly with NATO to service Afghan helicopters and train their crews.

MILITARY RELATIONS

U.S.-Russian military cooperation has included joint exercises, bilateral meetings, port visits and planning conferences.

Atlas Vision, for example, is an annual exercise aimed at improving the two nations’ ability to operate together in areas of mutual interest, such as joint peacekeeping tasks, coalition and regional stabilization operations, crisis-response, illegal weapons trafficking, search and rescue capabilities, counter-trafficking, and combating terrorism.

But the relationship has been an off-again, on-again affair.

The Pentagon announced early this month that it had put on hold all military-to-military engagements in light of events in Ukraine. Washington similarly suspended military cooperation following the August 2008 Russian-Georgian war. Bilateral activities resumed in July 2009.

Pentagon officials have stressed that despite the current break in programs, they are trying to keep lines of communication open. Defense Secretary Chuck Hagel has spoken to Russian counterpart Sergei Shoigu to tell him about U.S. concern about the intervention in Ukraine and warn that Moscow’s action risk further instability in the region and isolation from the international community.

NASA

Since the retirement of the U.S. shuttle fleet in 2011, the Russian Soyuz spacecraft has been the sole means to fly crews to and from the International Space Station.

NASA is paying nearly $71 million for a seat in Soyuz, and it will have to rely on Russia through 2017 before American companies provide an alternative crew transport capacity. That included a blast-off early Wednesday from Kazakhstan carrying one NASA astronaut and two Russian cosmonauts.

Russian officials have given no indication that they could curb cooperation with NASA amid the tensions, and it appears unlikely they would ever do so. For NASA, rejecting Russia’s launch services would mean putting its presence on the station on hold, something that is hard to imagine.

AGRICULTURE

Russia has been an important importer of U.S. meat and it has banned imports amid periods of tensions, citing technical reasons. Russia in 2013 banned imports of U.S. pork, though it is now accepting a few shipments that the USDA has certified are free of a growth hormone called ractopamine. Russia has said the existing U.S. system of checks don’t guarantee its safety. Similarly, Russia shut off all beef imports in 2013.

Russia also banned the imports of U.S. dairy products in 2010 over in a spat over customs requirements. The disagreement even played a role in the Sochi Olympics, when Russia refused to allow the United States to ship Chobani yogurt to its athletes in the Olympic village.

If tensions continue, bans on U.S. products will likely expand.

TRADE

America’s economic ties to Russia are relatively small, but analysts said economic retaliation by Russia could have an impact on particular U.S. companies and on the overall U.S. economy more generally.

Russia-U.S. trade stood at about $30 billion a year, a fraction of Russia-EU trade exceeding $400 billion. Russia, however, has been an important market for many major U.S. companies — from Coca-Cola and Procter & Gamble to General Electric and Boeing.

In 2013, Russia was America’s 28th-largest export market, buying $11.2 billion in goods, including $1.9 billion in civilian aircraft and aircraft parts and $1.3 billion in motor vehicles and parts. Other exports to Russia included everything from oil field drilling equipment to heavy machinery and medical instruments. Leading agricultural exports included meat and poultry products and soybeans.

U.S. imports from Russia totaled $27 billion in 2013, led by $16.2 billion in fuel oil imports. That gave the United States a $15.8 billion trade deficit with Russia last year.

Should the Obama administration impose additional sanctions, the risk of Russian retaliation against U.S. businesses would grow. “There are American jobs at stake, there are American business interests at stake,” said Cliff Kupchan, senior Russia analyst at the Eurasia Group.

OIL AND GAS

Exxon Mobil Corp. has signed a deal with Russia’s Rosneft that gives the U.S. company access to some of the world’s richest sources of oil and other hydrocarbons in the Black Sea and the Russian Arctic. The two companies are set to start exploration this year.

The alliance that also envisages multibillion dollar investments in energy projects in the Black Sea, Siberia and Russia’s far east, seems too big to be shaken by political storms.

Kupchan said U.S. companies currently doing business with Russia probably won’t be harmed, but if “competition began for a major new oil deal, a U.S. company probably wouldn’t be included.”

Many European nations have a heavy dependence on natural gas from Russia. Sung Won Sohn, an economics professor at California State University, Channel Islands, said that the biggest threat to the U.S. economy would come if Russia decided to target European nations for retaliatory sanctions such as cutting off energy supplies or increasing the prices of the shipments.

(AP)