Russia's Foreign Minister Sergei Lavrov on Monday dismissed as "counter-productive" an announcement by Washington that it could take extra measures to defend US-allied fighters in Syria.
At a news conference in Qatar, Lavrov condemned comments by the White House that it could take "additional steps" to protect allies in Syria and warned Bashar al-Assad's regime not to impede their actions.
"We believe it's counterproductive to announce publicly that some US-trained armed groups... will be under the protection of the coalition's air forces," Lavrov said.
"And that to protect these groups this air force would be authorised to strike at any forces which may -- may -- be considered a hindrance to the work of this group."
Lavrov added that the matter had been raised with US Secretary of State John Kerry when they met earlier Monday in Qatar's capital Doha.
Earlier, White House spokesman Josh Earnest said Syria "should not interfere" with operations by US-trained forces, warning that "additional steps" could be taken to defend them, raising the prospect of strikes against the regime.
In another apparent criticism of Washington, Lavrov said: "We are seriously concerned about the continuing crisis in Syria and the humanitarian disaster that has broken out in the country, and are in favour of an immediate end to external intervention in the Syrian crisis."
Lavrov added that the matter had been raised with Kerry.
Both Lavrov and his American counterpart were in the Gulf to hold a series of talks on wide-ranging matters including not only Syria, but also issues such as the Iran nuclear deal, "terrorism" and Yemen.
Lavrov held a tripartite discussion with Kerry and Saudi Foreign Minister Adel al-Jubeir.
He also met Hamas leader Khaled Meshaal in Qatar.
Also at Monday's news conference was Qatari Foreign Minister Khalid bin Mohammad Al-Attiyah, who said his country agreed "with our friends in Russia that the solution (in Syria) should be political".