The U.S.-led coalition said its warplanes or "partnered forces" may have been behind strikes that killed up to 28 civilians in eastern Syria.
Forces fighting for and against the Syrian government have blamed one another for violating a short-lived truce in eastern Ghouta.
"The actions of the U.S. coalition do not comply with legal norms. Beyond all doubt, it is an unprecedented act of aggression," one Russian senator said.
"It was all theater," said the U.S.-backed commander who has since switched his allegiance to Turkey.
As Tu-22M3 supersonic bombers blasted the last of ISIS in Syria, Russia announced the new Tu-22M3M fitted with missiles that can soar 130,000 feet and attack 620 miles away.
Major General Issam Zahreddine, who led his Syrian Republican Guard brigade for three years against an ISIS siege in Deir Ezzor, was reportedly killed by a landmine.
Syria's war is almost over and experts say the U.S. has few options to counter what's been a major victory for Russia, Iran and President Bashar al-Assad.
The Syrian military's Fifth Assault Corps, known as "ISIS Hunters," has made ISIS an offer it can't refuse.
In the video, a man identifies himself and a companion as Russian soldiers captured by ISIS during a counteroffensive against Syrian troops in Deir Ezzor.
Two rivals are battling ISIS in the jihadists' final stronghold of Deir ez-Zor. One seeks to return Syria to its former self; the other wants more power for Kurds.
Russian and U.S. allies are battling insurgents and jihadists trying to topple the Syrian government, but the latter wants to reshape the nation.
A monitoring group said the death toll in Deir Ezzor was likely to increase as many of those injured were in a critical condition.
Militants kidnap citizens after attacking government-held areas in the eastern Syrian city of Deir al-Zor.