Stepping into a region on edge, Vice President Joe Biden came to Poland on Tuesday to reassure anxious allies that the U.S. will stand up to Russia’s aggression in neighboring Ukraine, even as Moscow brushed aside stern warnings from the West and signed a treaty to annex Crimea.

Even as Biden arrived in Warsaw, Russian President Vladimir Putin was moving fast ahead with plans to absorb Crimea into its orbit, flouting fresh sanctions the U.S. and Europe imposed a day earlier. In a fiery speech in Moscow, Putin lambasted the West for sowing unrest in Ukraine.

But in Warsaw, it was all smiles as Biden greeted Polish Prime Minister Donald Tusk at the start of a two-day trip to Poland and Lithuania. The two leaders were to deliver statements after their meeting in what will likely mark the first U.S. response to a treaty signed Tuesday by Russian and Crimean leaders to clear the way for the peninsula to become part of Russia.

Russia’s move in clear defiance of its neighbors and the U.S. ups the pressure on Biden to convince its NATO allies that the U.S. won’t stand idly by.

Biden’s visit to the region is part of a broader U.S. campaign to send a clear signal to Putin following Sunday’s referendum in Crimea, which the U.S. has dismissed as illegal. In coordination with Europe, the Obama administration has frozen the U.S. assets of nearly a dozen Russian and Ukrainian officials. But Putin appears to have reacted with a shrug, and Obama’s critics contend the U.S. steps thus far amount to a slap on the wrist.

In meetings Tuesday in the Polish capital and later in Lithuania’s capital, Vilnius, Biden was to discuss the crisis with the leaders of Estonia, Lithuania and Latvia — three Baltic nations that are deeply concerned about what Russia’s military intervention in Ukraine’s Crimean Peninsula might portend for the region. All four countries share borders with Russia; Poland also borders Ukraine.

In Warsaw and Vilnius, Biden will affirm the U.S. commitment to defending its NATO allies, which includes Poland and the three Baltic states but not Ukraine. A senior administration official said the vice president will discuss ways to strengthen the alliance so NATO emerges even stronger from the crisis, and will echo Obama by insisting that if Russia continues to flout international law, the costs will only increase.

Biden will also discuss what additional steps the U.S. can take to shore up security for Poland and the Baltics, such as increased training, said the official, who wasn’t authorized to comment by name and demanded anonymity. At Warsaw’s request, the U.S. last week sent some 300 air troops and a dozen F-16 fighters to Poland for joint training in a show of military support for a key ally.

Also on the agenda: long-term energy security in Europe, a key factor that has confounded the West’s attempts to display a united front in punishing Russia. Much of Europe is heavily dependent on Russian natural gas, and European countries have major economic interests in Russia that could be in jeopardy if Moscow retaliates with sanctions of its own.

Biden plans to address energy diversification within Europe, but will also discuss how the U.S. can help, said the official, declining to offer more details

Republican lawmakers and a handful of European countries, including Poland, have urged the White House to accelerate approval of U.S. natural gas exports to help Europe wean itself off its dependence on Russia. The White House has insisted that would take too long to help the current crisis and says Russia is too dependent on gas revenues to cut off supplies to Europe.

One option that doesn’t appear to be on the table: rethinking the U.S. posture on missile defense in the region. Poland is still bruised from Obama’s 2009 decision to cancel the final phase of a defense system sorely desired by Poland as a hedge against Russian missiles. The official said Biden will reassure Poland that the smaller, phased-in system Obama chose instead is on schedule, but won’t be discussing potential changes.

(AP)