Hundreds of Iranian troops have arrived in Syria in the last 10 days and will soon join government forces and their Lebanese Hezbollah allies in a major ground offensive backed by Russian air strikes, two Lebanese sources told Reuters.

"The (Russian) air strikes will in the near future be accompanied by ground advances by the Syrian army and its allies," said one of the sources familiar with political and military developments in the conflict.

"It is possible that the coming land operations will be focused in the Idlib and Hama countryside," the source added.

The two sources said the operation would be aimed at recapturing territory lost by President Bashar Assad's government to rebels.

It points to an emerging 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 in rapid advances earlier this year.

"The vanguard of Iranian ground forces began arriving in Syria: soldiers and officers specifically to participate in this battle. They are not advisors ... we mean hundreds with equipment and weapons. They will be followed by more," the second source said. Iraqis would also take part in the operation, the source said.

Thus far, direct Iranian military support for Assad has come mostly in the form of military advisors. Iran has also mobilized Shi'ite militia fighters, including Iraqis and some Afghans, to fight alongside Syrian government forces. Lebanon's Hezbollah, which is backed by Iran, has been fighting alongside the Syrian army since early in the conflict.

Russian offensive in Syria continues

Russian jets launched a second day of air strikes in Syria on Thursday, targeting areas held by an insurgent alliance that includes a group linked to Al-Qaida, but not the Islamic State militants Moscow said it had hit.

Russia said it had launched eight air strikes with Sukhoi warplanes overnight, hitting four Islamic State targets. However, the areas where it said the strikes took place are not held by Islamic State.

Al-Mayadeen, a pro-Damascus television channel, said jets carried out at least 30 strikes against an insurgent alliance known as the Army of Conquest. The alliance includes the Nusra Front, Al-Qaida's Syrian branch, but not Islamic State, which has declared a caliphate on swathes of Syria and Iraq.

The Army of Conquest has been advancing against government forces in northwestern Syria in recent months, and has support from regional countries that oppose both Assad and Islamic State.

Russia's decision to join the war with air strikes on behalf of Assad is a major turning point in international involvement in the conflict.

The United States is leading a separate alliance waging an air war against Islamic State fighters, which means the Cold War superpower foes are now engaged in air combat over the same country for the first time since World War Two.

They say they have the same Islamic State enemies. But they also have very different friends, and opposing views of how to resolve a 4-year-old civil war that 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. Moscow supports the Syrian president and believes his government should be the centerpiece of international efforts to fight extremist groups.

Russia's first airstrikes in Syria, which Moscow said were aimed at Islamic State fighters, instead hit Free Syrian Army sites and killed dozens of civilians, an opposition Turkmen group said on Thursday.

Russian jets continued to bomb rebel positions for a second day in western Syria on Thursday. The bombardment marks a major escalation of the four-year conflict, where the United States and its coalition of Western allies and regional states have been flying missions for more than a year.

Areas where ethnic Turkmens live in Homs and Hama came under attack on Wednesday, the Turkey-based Syrian Turkmen Assembly said in a statement. In the village of Telbiseh near Homs alone, 40 civilians, including Turkmens, were killed, it said.

The Turkmens, whose Syrian Turkmen Brigades armed wing is allied with the Free Syrian Army, say they have been targeted by both Assad's forces and Islamic State since the civil war began in 2011.

"We strongly condemn Russia, which was not satisfied with its unlimited support of the murderous regime and now rains down bombs on the Syrian people, promising 'democracy'," the statement said.

The Syrian Turkmen Assembly was set up in Gaziantep, Turkey, to unite factions of the Turkish-speaking ethnic group present in Syria and is backed by the Turkish government, which has been an outspoken critic of Syrian President Bashar al-Assad.

