(Bloomberg) -- The U.S. and Russia pledged to maintain a fragile cease-fire set to expire Monday in Syria, including in the key city of Aleppo, in a bid to keep alive efforts to end five years of civil war.

The two countries “re-emphasized” terms with field commanders on all sides, especially in Aleppo, the Eastern Ghouta suburb of Damascus and the northwestern Latakia province, where “we are determined to improve and sustain” the cessation of hostilities, they said in a joint statement on Monday.

Russia, whose military intervention in Syria over seven months ago bolstered President Bashar al-Assad, also agreed to press the Syrian government to “minimize aviation” operations over areas mostly inhabited by civilians or rebel groups that have signed up to the cease-fire. The U.S. said it would work with regional allies to prevent terrorist groups smuggling weapons and fighters into Syria and together with Russia identify territory controlled by Islamic State and the al-Qaeda-linked Nusra Front, which aren’t part of the truce.

Geneva Negotiations

Peace talks in the Swiss city of Geneva collapsed last month after an upsurge in fighting, particularly in Aleppo, threatened to end a partial cease-fire brokered by Russia and the U.S. in late February. The Syrian conflict, which has killed at least a quarter of a million people and caused millions more to flee their homes, has handed Islamic State territory from which to plot terror attacks in Paris and Brussels and provoked the biggest refugee crisis in Europe since World War II.

Russia, whose air force is backing Syrian government troops, defended the Aleppo offensive as a response to attacks by Nusra and rebel groups working alongside it, demanding that opposition forces cut all ties with the al-Qaeda wing. Last week, though, it agreed to a truce in the northern city that was initially due to last 48 hours and was extended for another 72 hours from Saturday.

The Syrian opposition says Assad is determined to re-assert full control of Aleppo, once the country’s commercial capital and a key bastion of anti-government forces. Since April 22, Syrian rebels and military loyal to Assad traded rockets and bombs across Aleppo and its outskirts for around two weeks in clashes that killed 290 civilians, according to the Syrian Human Rights Observatory, a U.K.-based opposition monitoring group.

Russian Foreign Minister Sergei Lavrov spoke by phone on Monday with U.S. Secretary of State John Kerry. Lavrov urged rebel groups who enjoy support from the U.S. to end all links to terrorist groups as well as cut off supply routes for extremists from Turkey, according to the Foreign Ministry in Moscow. He also called for the resumption of the intra-Syrian talks in Geneva.

The U.S.-Russia statement demanded an end to “indiscriminate attacks on civilians, including civilian infrastructure and medical facilities.” On April 28, airstrikes on a hospital supported by Medecins Sans Frontieres in a rebel-held area in Aleppo killed at least 50 people, according to MSF. The Syrian opposition blamed government planes for the attack.

To contact the reporters on this story: Henry Meyer in Moscow at, Rachel Layne in Boston at To contact the editors responsible for this story: Bill Faries at, Balazs Penz at, Sarah McGregor

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