Russia has sent more than 50 military aircraft as well as marines, paratroopers and special forces into Syria, where it has launched air strikes against Islamic State militants, the defence ministry said on Thursday.
"More than 50 warplanes and helicopters are part of the Russian airforce striking Islamic State targets in Syria," defence ministry spokesman Igor Konashenkov told the Interfax news agency.
Russia on Wednesday waded into the multi-front conflict, launching air strikes against what Moscow said were IS militants battling its Soviet-era ally Syria.
In the run-up to the strikes, Russia had expanded its naval facility in the port city of Tartus and established a military base in Latakia, the stronghold of the beleaguered regime of Bashar al-Assad.
Konashenkov said marines, paratroopers and special force units would be mobilised to protect Russia's military assets.
On Monday, Russian President Vladimir Putin called for a broad UN-backed coalition to fight IS jihadists as he addressed the UN General Assembly for the first time in a decade.
Moscow has been pushing for a broader coalition to fight the Islamic State group to include allies of the Assad regime, an idea that the West has rejected.
Putin's proposal is seen as a direct challenge to US President Barack Obama who has vowed to crush IS and called on countries to join the United States in its campaign.
Moscow has ruled out joining the US-led coalition.
"Theoretically, it would look nice (to join the US-led coalition) from a political point of view, but I think that we have difficulty understanding the principles on which the coalition is acting," foreign ministry official Ilya Rogachyov said.
"On the basis that the coalition currently exists, we are unlikely to join," he told the state news agency RIA Novosti.
Russia has appointed Lieutenant General Sergei Kuralenko to represent Russia at the Baghdad-based intelligence task force Moscow is setting up with Iran, Iraq and Syria, a defence ministry spokesman said on Thursday.
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