Russian intervention has left the US with little room to manoeuvre as Syria’s changing battle lines become more complex.
At least 45 people have been killed when Russian fighter planes launched air strikes in western Syria, activists said.
The Syrian Observatory for Human Rights said the jets targeted the rebel-held Jabal al-Akrad region of the mainly regime-held Latakia province on Tuesday.
The activist group said civilians were amongst the casualties caused by the strikes but did not know exactly how many of the dead were non-combatants.
Rami Abdel Rahman, the director of the group, said dozens of people had also been wounded and that the number of dead could go up as those with serious injuries succumbed to their wounds.
He said those killed included rebel fighter and their families, and identified a rebel commander who died as chief of staff of the First Coastal Division group, a faction fighting under the banner of the “Free Syrian Army”.
Opposition forces have positions in the Jabal al-Akrad region, which is in the far north of coastal Latakia.
Latakia is home to the ancestral village of Syria’s President Bashar al-Assad and has been a key target of Russian air strikes since Moscow began an air campaign in Syria in September.
Russian President Vladimir Putin said on Tuesday that Moscow’s intervention in Syria demonstrates it can counter any threats.
“The operation has confirmed that Russia is ready to adequately and effectively respond to terrorist and any other threats to our country,” Putin said in a speech to military and intelligence commanders at the Kremlin, the AFP news agency reported.
Russia says it has hit some 500 “terrorist” targets since launching its campaign.
Russia says its strikes target the Islamic State of Iraq and the Levant (ISIL) group and other “terrorists”, but rebels and the US, which is conducting its own campaign against ISIL and some rebel factions, say Moscow has focused more on opposition forces than ISIL.