MOSCOW -- Russia has provided air cover to a leading Western-backed opposition group in Syria, President Vladimir Putin said Friday, calling for closer co-ordination with the U.S.-allied coalition -- comments that may reflect Moscow's desire to narrow its differences with the West over the Syrian crisis.

At the same time, Putin vowed to further modernize Russia's military and said its forces in Syria will "immediately destroy" any target threatening them, a strong warning to Turkey following its downing of a Russian warplane at the Syrian border.

Speaking at a meeting with top Defence Ministry officials, Putin said while supporting the Syrian government forces, Russia has backed some units of the Free Syrian Army, a Western-backed opposition group fighting Syrian President Bashar Assad's army.

"Several (FSA) units totalling more than 5,000 people, along with regular troops, are conducting offensive operations against terrorists in the provinces of Homs, Hama, Aleppo and Raqqa," Putin said. "We have provided air support for them as well as the Syrian army, helping them with weapons, ammunition and supplies."

While Putin sounded unequivocal, his spokesman Dmitry Peskov said a few hours later that the president meant to say that Russia is sending weapons and supplies to Syrian government forces and not the FSA, but provides air cover to both. Peskov's statement could be an attempt to assuage Assad, who calls the FSA and other moderate opposition groups "terrorists."

Putin and his officials said before that Russia had co-operated with the FSA, but the group's representatives have denied that.

If confirmed, Russian support for the FSA will represent a major policy shift for Moscow, which has been accused by the West of striking moderate rebels to back up Assad instead of its declared goal, the Islamic State group.

Asked to comment on Putin's claim, U.S. State Department spokesman John Kirby said that "it's unclear to us also, whether these -- these claims of support for the FSA are true." He reaffirmed that "the vast majority of airstrikes conducted by Russian military aircraft are against opposition groups to Assad and not aimed at ISIL."

"By and large, there's been no major change in calculus from what we've seen them hit, and they are largely continuing to hit opposition," Kirby added.

Asked whether the coalition should co-ordinate more with Russia, British Defence Minister Michael Fallon dismissed Putin's statements saying Moscow has to play a more constructive role in the political transition in Syria.

"What they've got to do is stop propping up the Assad regime, stop bombing opposition groups who are opposed to the Assad regime, stop dropping unguided munitions on innocent villages and groups who've been fighting Assad, and get behind the political process that is now under way of leading that country to a more pluralist government and a future without Assad," said Fallon, who was speaking at a press conference in the Pentagon alongside U.S. Defence Secretary Ash Carter.

Russia's Defence Minister Sergei Shoigu said Russian warplanes have flown 4,000 combat sorties in Syria since Moscow launched its air campaign on Sept. 30, destroying 8,000 "terrorist" targets. He added that Russia moved 214,000 metric tons of supplies to support the military action in Syria and helped restore a tank repair factory in the Syrian province of Homs.

Without naming Turkey, Putin said the military should respond in full force to any further "provocations." He said the Russian military base in Syria has been beefed up with additional aircraft and air defence weapons.

"I order you to act in the toughest way," Putin said. "Any targets threatening the Russian groups of forces or our land infrastructure should be immediately destroyed."

At the same time, he said the military should "develop co-operation with all countries, which have a real interest in destroying terrorists," specifically mentioning the need to co-ordinate with the U.S.-led coalition and Israel to ensure flight safety.

Speaking on a visit to Rome, Russian Foreign Minister Sergey Lavrov offered a rare praise for the U.S.-led coalition, saying Moscow is glad to see it has "intensified its activities," targeting oil facilities and trucks in IS-controlled territories. He emphasized the need to shut the Syrian border with Turkey, saying that Turkey's downing of a Russian warplane amounted to a "coverup of terrorists."

The downing of a Russian bomber by a Turkish fighter jet on Nov. 24 has badly strained relations between Moscow and Ankara.

Turkey said it downed the Russian plane after it violated its airspace for 17 seconds despite repeated warnings, while Russia has insisted the plane had remained in Syrian airspace. Putin has denounced the Turkish action, ordered the deployment of S-400 long-range air defence missile systems to a Russian base in Syria and introduced a slew of economic sanctions against Turkey.

Turkey's foreign minister said Friday his country is refraining from responding, but added the country's patience has limits. "If we are not responding to all that they have done until now, it is not because we are afraid or because of any psychology of guilt," Minister Mevlut Cavusoglu told NTV television.

Putin said the Russian military action in Syria is essential for protecting Russia from extremists based there. He has said between 5,000 and 7,000 citizens of Russia and other ex-Soviet nations have joined the Islamic State group.

"Our action there hasn't been prompted by some abstract geopolitical interests or a desire to train and test new weapons systems, which is important too," Putin said. "The main thing is to avert a threat to the Russian Federation."

Russia's ambitious arms modernization program has continued at full pace this year, even though low oil prices and Western sanctions drove the economy into recession. Shoigu said the military has received 35 new intercontinental ballistic missiles, 243 aircraft, 90 air defence systems and 1,172 tanks and other armoured vehicles in 2015.

He added the navy received two new nuclear-powered submarines equipped with intercontinental ballistic missiles, two general-purpose submarines and eight surface warships this year.

The military also expanded its presence in the Arctic, building several new bases and other military facilities there.

Bradley Klapper and Lolita C. Baldor in Washington, Nataliya Vasilyeva in Moscow and Suzan Fraser in Ankara contributed to this report.