Hundreds of Iranian troops have arrived in Syria to join a major ground offensive in support of President Bashar al-Assad's government, Lebanese sources said on Thursday, a further sign of the rapid internationalization of a civil war in which every major country in the region has a stake.
Russian warplanes, in a second day of strikes, bombed a camp run by rebels trained by the CIA, the group's commander said, putting Moscow and Washington on opposing sides in a Middle East conflict for the first time since the Cold War.
The US and Russian militaries were due to hold talks via video link to seek ways to keep their militaries apart as they wage parallel campaigns of air strikes in Syria, a US defense official said.
Russian jets struck targets near the cities of Hama and Homs in western Syria on the second day of their air campaign.
Moscow said it had hit Islamic State positions, but the areas it struck are mostly held by a rival insurgent alliance, which unlike Islamic State is supported by US allies including Arab states and Turkey.
Hassan Haj Ali, head of the Liwa Suqour al-Jabal rebel group which is part of the Free Syrian Army, told Reuters one of the targets was his group's base in Idlib province, struck by around 20 missiles in two separate raids. His fighters had been trained by the CIA in Qatar and Saudi Arabia, part of a program Washington says is aimed at supporting groups that oppose both Islamic State and Assad.
"Russia is challenging everyone and saying there is no alternative to Bashar," Haj Ali said. He said the Russian jets had been identified by members of his group who once served as Syrian air force pilots.
Russian Foreign Minister Sergei Lavrov said later that Moscow was targetting Islamic State and did not consider the U.S.-backed Free Syrian Army a terrorist group, adding that they should be part of a political solution in Syria.
The aim is to help the Syrian armed forces "in their weak spots," said Kremlin spokesman Dmitry Peskov.
Two Lebanese sources told Reuters hundreds of Iranian troops had reached Syria in the past 10 days with weapons to mount a major ground offensive.
They would also be backed by Assad's Lebanese Hezbollah allies and by Shi'ite militia fighters from Iraq, while the Russia would provide air support.
"The vanguard of Iranian ground forces began arriving in Syria: soldiers and officers specifically to participate in this battle. They are not advisers ... we mean hundreds with equipment and weapons. They will be followed by more," one of the sources said.
So far, direct Iranian military support for Assad has come mostly in the form of military advisers. Iran has also mobilized Shi'ite militia fighters, including Iraqis and some Afghans, to fight alongside Syrian government forces.
SAME ENEMIES, DIFFERENT FRIENDS
Russia's decision to join the war with air strikes on behalf of Assad, as well as the increased military involvement of Iran, could mark a turning point in a conflict that has drawn in most of the world's military powers.
With the United States leading an alliance waging its own air war against Islamic State, the Cold War superpower foes, Washington and Moscow, are now engaged in combat over the same country for the first time since World War Two.
They say they have the same enemies - the Islamic State group of Sunni Muslim militants who have proclaimed a caliphate across eastern Syria and northern Iraq.
But they also have very different friends, and sharply opposing views of how to resolve the 4-year-old Syrian civil war, which has killed more than 250,000 people and driven more than 10 million from their homes.
Washington and its allies oppose both Islamic State and Assad, believing he must leave power in any peace settlement.
Washington says a central part of its strategy is building "moderate" insurgents to fight against both Assad and Islamic State, although so far it has struggled to find many fighters to accept its training.
Moscow supports the Syrian president and believes his government should be the centerpiece of international efforts to fight extremist groups.
It appears to be using the common campaign against Islamic State as a pretext to strike against groups supported by Washington and its allies, as a way of defending a Damascus government with which Moscow has been allied since the Cold War.
The Russian strikes represent a bold move by President Vladimir Putin to assert influence beyond his own neighborhood: it is the first time Moscow has ordered its forces into combat outside the frontiers of the former Soviet Union since its disastrous Afghanistan campaign in the 1980s.
In the second day of strikes, Russia said it launched eight sorties with Sukhoi warplanes overnight, hitting an ammunition depot near Idlib, a three-story Islamic State command center near Hama and a car bomb factory in the north of Homs. None of those areas has a large presence of Islamic State.
Al-Mayadeen, a pro-Damascus television channel based in Lebanon, said the jets carried out at least 30 strikes against an insurgent alliance known as the Army of Conquest. The alliance includes the Nusra Front, Al Qaeda's Syrian branch, but not Islamic State.
The station later said Russian forces had also struck Islamic State positions in Raqqa province in the east. This could not be immediately confirmed.
The Russian and Iranian intervention in support of Assad comes at a time when momentum in the conflict had swung against his government and seem aimed at reversing insurgent gains.
"The Russian strikes are a game changer. Damascus is off the hook," a diplomat tracking Syria said.
The Army of Conquest in particular has been advancing against government forces in northwestern Syria, supported by regional countries that oppose both Assad and Islamic State.
Russia says its air strikes, unlike Washington's, are legitimate because they have Assad's blessing, and more effective because they can coordinate with government forces to find targets.
Prime Mininster Haidar al-Abadi of neighboring Iraq, where Washington is also leading an air war against Islamic State while Iran aids government forces on the ground, said he would be open to Russian strikes as well.
In Syria, insurgent-held Idlib province is of particular strategic importance to the government because it is close to Assad's heartland on the Mediterranean coast, where Russia also has its only Mediterranean naval base.
A Syrian military source said on Thursday that Russian military support would bring a "big change" in the course of the conflict, particularly through advanced surveillance capabilities that could pinpoint insurgent targets.
Putin's gamble of going to war in Syria comes a year after he defied the West to annex Ukraine's Crimea peninsula, drawing US and EU economic sanctions while igniting a wave of popular nationalist support at home.
He appears to be betting that decisive action to aid Assad will improve Russia's position at future talks on a political settlement, safeguard its control of the naval base and limit the influence of regional rivals like NATO member Turkey. It could also help his image at home as a strong leader willing to challenge global rivals, first and foremost the United States.