Hundreds of Iranian troops have reportedly crossed into Syria ahead of a ground operation supporting Bashar al-Assad against his enemies.

Sources in Lebanon claim that the soldiers arrived 10 days ago and will be supporting government forces, alongside fighters from the Shia Islamist group Hezbollah, against rebels in northern Syria.

An anonymous official told Reuters the operation was being mounted in conjunction with Russian air strikes and aimed to recapture territory lost by the Syrian regime.

Volunteers from Syria Civil Defence, also known as the White Helmets, help civilians after Russia carried out its first airstrikes in Syria

“The (Russian) air strikes will in the near future be accompanied by ground advance by the Syrian army and its allies,” one of the sources said. “It is possible that the coming land operations will be focused in the Idlib and Hama countryside."

Iran is believed to already have troops backing government forces in Iraq, where Shia militias believed to be funded by the Iranian government are also fighting Isis.

The Kremlin had already announced the creation of an operations centre in Baghdad where its forces will work with the Iranians and intelligence operatives from Iraq and the Syrian regime.

Putin with President Assad in 2005 (Getty Images)

Officials have insisted that no Russian troops will be deployed on the ground but Vladimir Putin has sent fighter jets, artillery, tanks and equipment to Assad.

The Syrian President had asked his Russian counterpart for military assistance to combat “terrorism”, although the term is used by the Syrian regime to refer to anyone opposing it.

Activists in territories held by non-Islamist rebels have claimed that they have been targeted by Russian air strikes in Homs and Hama, and American and French officials have accused Russia of targeting President Assad’s rivals.

An alliance of extremist groups including Jabhat al-Nusra and Ahrar al-Sham made rapid gains in Idlib province earlier this year, completely expelling the government from the area bordering Turkey.

Senator John McCain said today that he could “absolutely confirm” that Free Syrian Army rebels who had been funded and trained by the CIA were among those hit on Wednesday.

Mr Putin’s spokesperson has admitted Isis was not the only group being targeted, saying that “well-known” organisations had been chosen in co-ordination with the Assad regime.

Khaled Khoja, head of the Syrian National Council opposition group, told the UN that Russian strikes killed 36 civilians on Wednesday.

“It was very obvious that the Russian intervention was to support the regime, to support more killings inside Syria, and will create a more chaotic atmosphere," he said.

Mr Putin denied claims that his air force had killed civilians, calling the reports “information attacks” and saying they surfaced before Russian planes took off.