U.S. officials said Monday that the United States and Russia have agreed on a plan for a cease-fire in Syria starting Saturday that would exclude attacks on the Islamic State group and al-Qaida’s local affiliate.

The officials said that the two sides have agreed on the terms and conditions for the “cessation of hostilities.” A formal announcement is expected after Presidents Barack Obama and Vladimir Putin speak on the matter by telephone. The officials weren’t authorized to speak about the matter publicly and demanded anonymity.

The announcement would cap weeks of diplomacy that intensified in the past few days, aimed at reaching a temporary truce that would allow the parties to return to the negotiating table in Geneva. A first round of indirect talks collapsed rapidly last month after the government launched a massive offensive backed by Russian airstrikes in the northern province of Aleppo, near the Turkish border.

The leader of a Saudi-backed Syrian opposition alliance said in a statement that rebel factions have agreed “in principle” to an internationally mediated temporary truce. Riad Hijab did not elaborate on the terms, but called on Russia, Iran and the Syrian government to stop their attacks, lift blockades and release prisoners held in Syria.

Residents of the Syrian capital earlier Monday expressed skepticism about talk of a “provisional agreement” for a truce, a day after a wave of Islamic State bombings killed about 130 people in government-held areas near Damascus and another city.

Details of the tentative cease-fire between the government and insurgents, announced in Jordan on Sunday by U.S. Secretary of State John Kerry, have not been made public. Even if a truce were to take hold, IS would not be a party to it.

The Russian Foreign Ministry put out a statement earlier Monday saying that Foreign Minister Sergey Lavrov and Kerry spoke two more times by telephone on Sunday and agreed on the parameters for the cease-fire.

The statement said those parameters were then reported to Putin and Obama. No further details were immediately available.

The U.N.’s special envoy for Syria, Staffan de Mistura, told The Associated Press on Monday that this week is shaping up as “crucial” for diplomatic efforts to help end the fighting, though he declined to provide details of the negotiations.

Sunday’s blasts that ripped through the Sayyida Zeinab suburb of Damascus and the central city of Homs were among the deadliest bombings in government-held areas in Syria’s devastating civil war.

The Islamic State group claimed both attacks. The extremists are dug in on the outskirts of the two cities and have repeatedly targeted pro-government strongholds.

De Mistura condemned the bombings and said it suggested the group is feeling “cornered” amid an intensified diplomatic push to end the five-year war. The U.S. also condemned the “barbaric terrorist attacks.”

Inside the Hamidiyeh Souk, a popular Damascus bazaar which is typically crowded with shoppers, people said they were worried that a cease-fire would not be evenly observed and could leave the Syrian authorities vulnerable.

“I hope there will be no cease-fire, because if there is a cease-fire, Turks will increase their support for criminals and traitors,” said Ahmad al-Omar from the northern Aleppo province, adding that Turkey may seek to let opposition fighters in via its border with Syria.

Others at the bazaar echoed President Bashar Assad’s statements that a cease-fire could give an advantage to rebel forces and the Islamic State group.

“I believe that those proposals now are … a pretext to stop the advance of the Syrian army, which is trying to liberate the homeland,” said Ahmad al-Issa.

The Associated Press reported from the bazaar on a government-approved visit.

On Monday, the Kremlin announced that Putin spoke with the emir of Qatar, a key supporter of the rebels fighting to topple Assad. The two sides agreed “to intensify bilateral contacts at various levels to facilitate the settlement of the crisis,” the statement said. Putin also discussed Syria with King Salman of Saudi Arabia, another leading backer of the rebels, in a phone conversation on Friday.

Syrian officials said the government was ready to take part in a truce as long as it is not used by militants to reinforce their positions. Syrian troops backed by Russian warplanes are waging a major offensive in the northern Aleppo province, trying to seal the border with Turkey, a key supporter of the rebels, before any truce is reached.

Meanwhile, the Syrian government’s supply route by land to the city of Aleppo was cut by heavy fighting Monday as the army, supported by allied militias and the Russian air force, fought to consolidate its recent gains in the northern province.

The Britain-based Syrian Observatory for Human Rights, which relies on a network of contacts to monitor the war, said Islamic militias assaulted government-held positions around Khanaser, a town southeast of Aleppo, setting off intense clashes that have lasted through the day. Khanaser lies along the government’s only access route to the city.

Fighting has been fierce in Aleppo province in recent weeks amid a government offensive to cut off the rebel stronghold.

Among the youth sitting around the Syrian capital’s landmark Omayyad mosque, at the entrance of the old souks, few wanted to talk politics.

Those who did expressed their wariness of a political solution after several rounds of unsuccessful peace talks. “It’s good for the Syrians to stop fighting but it will not happen, said Awuj Aqeel, a student.

“Every time they agree on a truce for a period of time and then they break it.”

(AP)