Thousands of Iranian, Afghan and Iraqi fighters have arrived in Syria to defend Damascus and its suburbs against Islamic State (IS), which has said it will mount an offensive against the capital following recent battlefield successes in Deir al-Zor and Palmyra.

So far, 7,000 have reportedly been positioned around the city. They are expected to go on the offensive to retake from fundamentalist militiamen the suburb of Jobar from which they can easily access the eastern gates of the city.

The total number of reinforcements sent by Iran could rise to 15,000 when fighters reach the northern port of Latakia to defend the government-controlled coastal region from assaults by al-Qaeda affiliate Jabhat al-Nusra, which has imposed its rule over most of the northern Idlib province on the Turkish border.

Iran’s state news agency Irna has quoted the head of the elite Quds force of the Revolutionary Guards, as saying, “In coming days the world will be surprised by what we are preparing in co-operation with Syrian military leaders.”

Defence agreement

Fearing overt involvement by ground forces could harm chances of a deal over its nuclear programme, Tehran hesitated to act until it became clear that the Syrian army and its militia allies could not continue to contain IS and al-Qaeda affiliate Jabhat al-Nusra.

Shia Iran was also loath to transform the Syrian war into the Shia-Sunni sectarian conflict that Sunni Saudi Arabia and its allies claim it is.

In March, Nusra received injections of funds and guns – which found their way to IS – from Saudi Arabia, Qatar and the US as well as an influx of fresh fighters routed through Turkey. US-supplied artillery shells, mortars and Tow anti-tank missiles were key to the battle for Idlib in April and continue to account for advances of the so-called Army of Conquest, which has taken control of most of Idlib.

Free Syrian Army

Nusra has been the main beneficiary as it has made Idlib its main base. Under orders from al-Qaeda central in Pakistan, Nusra has attempted to integrate with local Syrian forces. This policy contrasts with that adopted by IS, which relies on foreign fighters who, in some locations, constitute 60 per cent of deployment.

While al-Qaeda’s leader Ayman al-Zawahiri has tried to create and maintain a distinction between Nusra and IS, this fails on the ground when the two join forces in battle or fighters migrate with their weapons from one to the other, as they did recently during the struggle for the Yarmouk quarter south of Damascus.

Forces welcomed

Iran initially backed the government because of a long-standing strategic alliance which dates from 1980, the onset of the eight-year Iran-Iraq war when Syria sided with Tehran rather than Baghdad. Although the Syrian Baathist regime adopted this stand because of its bitter rivalry with the Iraqi Baathist government, Damascus’s alliance with Tehran alienated the Saudis and its Gulf partners which financed the Iraqi war effort.

Tehran’s decision to send fighters is motivated not only by concern over the establishment of expanding IS and Nusra extremist Sunni entities in Syria and Iraq but also because these groups could unseat the pro-Iranian secular Syrian regime and the Shia fundamentalist government installed by the US in Baghdad, shrinking Iran’s sphere of influence in the region.

Iranian president Hassan Rouhani – who is regarded as a moderate – has said Tehran will stick with the Damascus government “until the end of the road”.