De Mistura's separate meetings with Syrian opposition and government representatives have yielded little outcome after four days of talks.
"Numerous" Syrian soldiers have been killed in a U.S. air strike near the Jordanian border, state television said on Friday.
Coalition fighter planes struck the convoy near the southern Syrian town of al-Tanf while it was advancing inside a protected "deconfliction zone" on Thursday - a move that US officials have claimed was a defensive measure to protect their forces at Tanf airbase.
Gatilov said he was referring to a strike on Wednesday May 17, not the air strike on Thursday.
His comments echoed an earlier statement by a deputy, Gennady Gatilov, who said the coalition's strikes on Syrian forces were "unacceptable" and could hinder peace talks. The coalition's headquarters argued that the forces had posed a threat to the United States and its allies.
The Syrian government, which has launched an offensive in the country's south backed by allied militias such as Iranian paramilitaries and the Lebanese Hezbollah group, has vowed to reach the border area with Iraq.
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In particular, she mentioned the labour and environment chapters as areas that would benefit from modernization. She says almost nine million United States jobs depend on trade and investment with Canada.
"This was despite Russian attempts to dissuade pro-regime movement towards al Tanf, coalition aircraft show of force and warning shots".
"All this, of course, is taking place [the U.S. coalition's strike on Syrian pro-government forces] amid growing calls from Washington and a number of other Western capitals to stop all contacts with Bashar Assad".
"The Syrian Arab Army is fighting terrorism on its territory, and no party has the right to determine the course of its operations", the Syrian military source added.
A second official told the broadcaster: "They were building a fighting position close to a U.S. coalition base". The area has been considered a de-conflicted zone under an agreement between the USA and Russian Federation earlier this month.
In an email to The Associated Press, the US -led coalition's press office said that Syrian pro-government "forces must now withdraw outside of the established de-confliction zone to avert further Coalition action and remove the threat to our forces".
"If people take aggressive steps against us, and that's been going on, it's policy of ours for a long time".