Syria's military has confirmed a 48-hour cease-fire in the northern city of Aleppo after U.S. officials announced an agreement had been reached with Russia.

A statement by the Syrian Armed Forces aired on Ikhbariya TV said the cease-fire will begin at 01:00 a.m. Thursday local time. It did not elaborate.

The announcement was slightly different than the one that came from U.S. officials, who said that the United States and Russia have persuaded Syria's government and moderate rebels to extend a fragile truce to Aleppo, where violence has escalated in recent days amid the country's brutal five-year-old civil war.

CBS News correspondent Margaret Brennan reports the U.S. and Russian militaries hammered out a deal to delineate areas in Aleppo that are still fair game for attack such as places where al Qaeda-linked Nusra Front is in control. Their proximity to the U.S.-backed rebels has been a problem.

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The officials say they have seen a decrease in violence since then but acknowledge that violations persist in some areas. The agreement on Aleppo follows an earlier deal to reaffirm the truce in the Damascus suburbs and coastal Latakia province.

The U.N. envoy for Syria said Wednesday that the alternative to a cease-fire in Aleppo is "catastrophic," raising the possibility that 400,000 people could head for the Turkish border.

Staffan de Mistura said after meeting the German and French foreign ministers in Berlin on Wednesday that Syrians say they need a cease-fire restored.

He said "the test is Aleppo now." He added that "the alternative is truly quite catastrophic, because we could see 400,000 people moving toward the Turkish border."

At the U.N., the Security Council met in emergency session on Wednesday, at the request of Britain, France, the U.S. and Ukraine, reports CBS News' Pamela Falk.

"The bottom line is that attacks on civilians and civilian infrastructure need to stop immediately," Stephen O'Brien, Under-Secretary-General for Humanitarian Affairs, and Emergency Relief Coordinator told the Council.

Many Western leaders have blamed the cease-fire's failure on Syrian President Bashar Assad.

"Through his actions, Assad has shown he has no commitment to a political settlement," U.K. Ambassador Matthew Rycroft said.