Turkish Prime Minister Ahmet Davutoglu on Friday accused Russia of targeting moderate Syrian rebels in its air strikes in Syria to prop up the regime of President Bashar Assad.

Speaking to Turkish reporters on his plane as he returned from the U.N. General Assembly in New York, Davutoglu rejected Moscow's insistence that its campaign of air strikes launched this week was aimed at Islamic State (IS) jihadists.

Two children were among at least seven civilians killed in air strikes carried out by Russian warplanes in Syria's northwestern province of Idlib, a monitoring group said Friday, citing witnesses.

"Four civilians, including a child and a woman, were killed in raids conducted by Russian military aircraft," said the Syrian Observatory for Human Rights.

Syrian rebels who oppose both the regime and the Islamic State group have been hit hardest by Russian air strikes, showing Moscow's determination to defend President Bashar Assad against all enemies, analysts say.

More than four years into Syria's devastating war, Russian warplanes began air strikes there on Wednesday, saying they were targeting IS jihadists and "other terrorist groups."

Syria cannot be forced to choose between President Bashar Assad and "terrorist groups" like the Islamic State (IS) organization, Turkish President Recep Tayyip Erdogan said Thursday.

Erdogan -- who has always rejected cooperation with Assad as a solution in the fight against IS -- was addressing the Turkish parliament as Russia launched air strikes in Syria in support of the regime.

Russian warplanes conducted air strikes on CIA-backed groups in Syria, U.S. Senator John McCain said Thursday, a claim which if true could mark an escalation in tensions between Moscow and Washington.

"Their initial strikes were against the individuals and the groups that have been funded and trained by our CIA," McCain told CNN, adding that the move showed Moscow's real priority: to "prop up" Syrian President Bashar Assad.

Russian warplanes unleashed a new wave of strikes against opponents of Syrian President Bashar Assad Thursday, as Moscow and Washington sought ways to avoid confrontation between their forces.

It was the second straight day of Russian raids in Syria, where Moscow has launched its first military engagement outside the former Soviet Union since the occupation of Afghanistan in 1979.

Four former senior Turkish prosecutors and an ex-military commander went on trial Thursday over the interception last year of an alleged consignment of arms bound for Syria, with the court immediately imposing a secrecy order on the hugely controversial case.

The case goes to the heart of claims -- repeated on occasion by the West but denied by Turkey -- that Ankara has worked far too closely with Islamist rebels in the hope of ousting Syrian President Bashar Assad.

The Pentagon will launch talks with the Russian military Thursday to discuss ways to avoid mishaps between planes from the U.S.-led coalition and Moscow, a defense official said.

The United States has repeatedly stressed the urgent need for Russia to communicate with it about when and where it plans to fly its fighter jets and bombers.

The General Security Department said on Thursday that it has arrested a Lebanese man for providing arms to terrorists and for sheltering them.

Sh. H. was arrested on charges of supplying terrorist groups with arms and ammunition, for storing them on their behalf and transporting them to Syrian territories, the General-Directorate of General Security said in a communique.

France demanded Wednesday that Russia confirm the targets of its air strikes in Syria, amid concerns they may not have been aimed at the Islamic State group, before accepting the enlarged coalition Moscow wants.

"Of course, we must fight together as hard as we can against Daesh," French Foreign Minister Laurent Fabius told reporters in New York, using the group's Arabic acronym.