Speaking in Moscow, Lavrov said Russia has waited long enough for Syria's moderate opposition to leave areas controlled by jihadist groups, and that air raids by Russia should "not be a surprise".
"What is happening in Aleppo and around it now, we warned the Americans about this in advance, and they know that we will be actively supporting the Syrian army from the air to prevent terrorists from seizing territory," he told a press conference.
Washington "is asking us and Syrian leadership to delay air strikes" until opposition forces are separated from jihadists of the Islamic State group and Al-Qaeda-linked Al-Nusra Front, he said.
"We believe there has been more than enough time" for that, he said.
"Everyone who has not left the terrorists now only have themselves to blame."
"We will be deciding on how our air force should act based on our understanding of the situation," he said.
"We share this understanding with the Americans during video-conferences... There won't be any surprises for the Americans."
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In Washington, a State Department spokeswoman insisted US officials are in talks with groups on the ground to encourage moderate elements to separate themselves from Al-Nusra.
"We would reiterate that Russia and the Assad regime need to distinguish between the terrorists and parties to the cessation of hostilities," Elizabeth Trudeau warned.
At the weekend, the Russian defence ministry unusually dispatched several statements marked "urgent" about clashes and massing "terrorist" forces near Aleppo, even suggesting the presence of Turkish troops.
Earlier Monday, the ministry said there were over two thousand militants near the Sheikh Maqsud neighbourhood, among them "various terrorist groups and teams of so-called 'moderate opposition'," accusing them of killing dozens of civilians.
Aleppo is divided between government and rebel control and has seen some of the worst fighting, which has thwarted diplomatic efforts to get the sides to move towards peace.
The Britain-based Observatory of Human Rights said Sunday that regime strikes on rebel-held districts in the city killed at least 32 civilians, while rebel attacks killed eight in neighbourhoods under government control.
Russia and the United States brokered a ceasefire on February 27 that dampened violence in Syria, but Aleppo remains a hotspot where fighting began to rage since mid-April compromising diplomatic efforts.
Russia has rolled back its air strikes after announcing a surprise pullout of the bulk of its forces in March, but it still maintains a contingent in Syria and flies air raids in the country.