The United States and its European allies say it is up to Russia to bring about a cease-fire in Syria, warning that patience with Moscow was "not unlimited."
The foreign ministers of Britain, France, Germany, Italy, and the United States and the EU’s foreign-policy chief issued a joint statement after meeting in New York on September 24.
"The burden is on Russia to prove it is willing and able to take extraordinary steps to salvage diplomatic efforts to restore a cessation of hostilities, allow unfettered humanitarian assistance, and create the conditions necessary for the resumption of UN-led talks about a political transition," the statement said.
The ministers also pressed the UN Security Council to "take urgent further steps to address the brutality of this conflict," particularly the military escalation in the northern city of Aleppo.
The Security Council is due to meet later on September 25 in New York at the request of Britain, France, and the United States.
A weeklong cease-fire brokered by the United States and Russia ended on September 19, and efforts to revive it have failed.