A U.S. official added to the criticism of Russia's military campaign in Syria, saying Wednesday only 30 percent of Russian airstrikes have targeted Islamic State militants.
Western nations have accused Russia of focusing its strikes on Syrian opposition fighters in support of its ally, President Bashar al-Assad, a charge Russian officials have denied.
U.S. envoy Brett McGurk, who met with U.S. and Iraqi military leaders in Baghdad Wednesday, said the other 70 percent of Russia's airstrikes in Syria have hit opposition groups.
More focused attacks
The Pentagon noted last month that Russian airstrikes had appeared more focused on Islamic State targets, after definitively linking the extremist group to the bombing of a Russian jetliner in late October.
Meanwhile, Russia said Tuesday for the first time it used missiles fired from a submarine in the Mediterranean to strike Islamic State targets in northern Syria.
In a televised meeting, Defense Minister Sergei Shoigu told President Vladimir Putin that cruise missiles targeted two positions near the extremist-controlled Syrian city of Raqqa.
"We can say with complete confidence that fairly serious damage was done to weapons stores and a factory for preparing [land] mines," Shoigu said, adding that oil infrastructure near the Turkish border was damaged as well.
Shoigu said more than 600 suspected IS targets have been struck by Russian warplanes in the past three days.
He also reported that Russian bombers were under fighter jet escort, as Putin ordered earlier this month following Turkey's November 24 shootdown of a Russian bomber that allegedly veered into Turkish airspace.
Tuesday's televised meeting came as Russian media reported that Russian and Syrian special forces had cleared the last remaining wreckage of the SU-24 bomber near the Turkish border, including the jet's flight recorder.
Putin is seen instructing Shoigu that investigators should only open the recorder in the presence of international experts, "to carefully document everything."
The French news agency AFP reported that Putin has invited British experts to help analyze the black box of the downed jet.