Russia said Thursday it did not intend to join the US-led coalition fighting the self-styled "Islamic State" in its current form, Russia's foreign minister said Thursday.

"We cannot be part of the coalition which operates without a mandate from the UN Security Council and the permission of the country whose territory it operates," Foreign Minister Sergei Lavrov told reporters Thursday.

The minister's statement comes as Russian military jets carried out a second day of strikes in Syria. US officials and activists on the ground claimed that the targets included rebels backed by the United States as concerns grew about a conflict that has now drawn in airpower from the world's two most powerful militaries.

Indeed, with American and allied airstrikes daily, and now Russian warplanes in the Syrian airspace, the war is taking on a dangerous new dimension.

US Senator John McCain on Thursday said Russia's initial air strikes in Syria targeted a rebel militia backed by Washington.

"I can absolutely confirm to you that they were strikes against our Free Syrian Army recruits that have been armed and trained by the CIA because we have communications with people there," McCain, head of the Senate Armed Services Committee, said in an interview with US broadcaster CNN.

The UK-based Syrian Observatory for Human Rights said Thursday's airstrikes in the central province of Hama hit locations of the CIA-backed rebel group, Tajamu Alezzah, as well as the province of Idlib, which is controlled by a coalition of rebel groups that include al-Qaeda's affiliate in Syria, Jabhat al-Nusra.

Report: Iranian troops massing in Syria

Iran's Foreign Ministry said it fully supports Russian airstrikes against "terrorist groups" in Syria. That statement follows reports by the Reuters news agency that, according to unnamed Lebanese sources, hundreds of Iranian troops will soon join government forces and their Lebanese Hezbollah allies in a major ground offensive backed by Russian air strikes.

"The (Russian) air strikes will in the near future be accompanied by ground advances by the Syrian army and its allies," one of the sources familiar with political and military developments in the conflict told Reuters. "It is possible that the coming land operations will be focused in the Idlib and Hama countryside," the source added.

The two sources said that the Iranian soldiers had arrived in the past 10 days and were planning a campaign to recapture territory lost by President Bashar al-Assad's government to rebel militas.

If confirmed, such a development would mean a military alliance between Russia and Assad's other main allies - Iran and Hezbollah - focused on recapturing areas of northwestern Syria that were seized by insurgents backed by the US and Gulf Arab states and Turkey in what is emerging as a regional proxy war backed by regional and global military powers.

Conflicting signals from Kremlin

Russia has denied inflicting any civilian casualties but has sent mixed signals over who the ultimate target of its ongoing military operations are.

Russian President Vladimir Putin's spokesman, Dmitry Peskov, said Russia was going after Islamic State militants as well as a "list" of other groups.

"These organizations are well known and the targets are chosen in coordination with the armed forces of Syria," he said Thursday, without elaborating.

A day before, however, Sergei Ivanov, Putin's chief of staff, said "the operation's target is solely air support for the Syrian government forces in their fight against ISIS."

Defense Minister Igor Konashenkov said Russian aircraft damaged or destroyed 12 targets in Syria belonging to the Islamic State group including a command center and two ammunition dumps.

Konashenkov said Russian Su-25M and Su-25 jets flew 20 sorties between Wednesday and Thursday morning.

Meanwhile in Paris, Russian Ambassador Alexander Orlov insisted that Russian warplanes in Syria were hitting at the same extremists targeted by the US and denied American claims that its military failed to coordinate the airstrikes.

Orlov said the targets were installations for IS and Jabhat al-Nusra, "two terrorist organizations recognized as such."

Washington and Moscow have agreed on the need to fight IS but not about the legitimacy of Syrian President Bashar al-Assad.

The Syrian civil war, which grew out of an uprising against Assad, has killed more than 250,000 people since March 2011 and sent millions of refugees fleeing to other countries in the Middle East and Europe.

jar/kms (Reuters, AFP, AP)