Russia allegedly bombed US-backed rebels in southern Syria, an official in Washington said on 16 June, Thursday.
The official who requested anonymity said, "Today, Russian aircraft conducted a series of airstrikes near al-Tanf against Syrian Counter-ISIL forces that included individuals who have received US support.
"Russian aircraft have not been active in this area of southern Syria for some time, and there were no Syrian regime or Russian ground forces in the vicinity,
"Russia's latest actions raise serious concern about Russian intentions. We will seek an explanation from Russia on why it took this action and assurances this will not happen again.?"
Meanwhile, Russia's foreign minister Sergey Lavrov on 16 June at an economic Forum in St Petersburg accused US of sparing al-Qaeda affiliate Jabhat al-Nusra to overthrow President Bashar al-Assad.
He argued that the reluctance of Washington to cut ties and distance itself from al-Nusra is one of the major reasons for the continuing fighting.
Lavrov said the United States could be "playing some kind of game here, and they may want to keep al-Nusra in some form and use it to topple the regime."
He added that he discussed the issue in a phone conversation recently with US Secretary of State John Kerry, who denied having any such plans. "But why then the Americans with all their potential can't force the units they have been working with to leave the territories controlled by bandits and terrorists," the Telegraph reported.
On Wednesday (15 June), John Kerry said that the US is losing its patience with Russia and added, "in fact, it is very limited with whether or not Assad is going to be held accountable." A ceasefire negotiated by US and Russia in February has been violated multiple times by all sides especially in many parts of Aleppo and other provinces. Al-Nusra and Islamic State (Isis) were not a part of the truce.