Islamic State advances on Homs in serious threat to Assad "So after the Sha'ar company and the positions surrounding it became part of the land of the Caliphate, the soldiers advanced, conquering new areas, and all praise is due to Allah," Islamic State said in the message. Even more concerning for the regime, the jihadists have now moved to assault Tayfur military airbase - perhaps the biggest and most valuable military stronghold still in the possession of the government in Damascus. According to the government's own propaganda video, which aired on Syrian State television, the base is home to SU-22M4, SU-22M2 and MiG-29 fighter planes, as well as air defence radars. It also said to house surface to air missile systems. Khodair Khashfa, a Syrian activist who spoke from Homs using a pseudonym, confirmed that Isil had taken full control of al-Sha'ar, and was now fighting at Tayfur airbase. "After Isil took over al-Sha'ar field they started to target Tayfur military airport," he told The Telegraph. They used a suicide car bomb on the front entrance of the base and, at the same time shelled the airport with Grad rockets and other artillery. The attacks represent a significant expansion in the presence and activity of the jihadists in central Syria. Whilst the heartland of Isil's control is Raqqa - a city located in remote deserts to the northeast of the country, which the regime appears to have written off - this onslaught is taking place at the heart of the axis of the remaining territory it controls. Homs intersects the central highway leading from the capital Damascus to Latakia, the area populated by the Alawite sect that the regime sees as its mainstay of support. "For a long time Isil has been keen to expand its presence further south and Homs makes sense as a platform for that," said Charles Lister, a Syria analyst. The choice of this location puts pressure on the Syrian regime, and also demonstrates that Isil has a reach that the rest of the Syrian opposition is incapable of demonstrating. Homs is both the city that the regime has touted as proof of its continuing power, and the historical heartland of the opposition in the current civil war. In 2011 when the war in Syria began, Homs was known as the "capital of the revolution," representing one of the main strongholds of anti-Assad fervour, which suffered some of the worst of the regime's retribution. For almost three years opposition fighters held out on the city's old town and other districts, but, besieged, starving and enduring daily bombardment, the fighters were eventually forced to surrender. Operations in Homs may also be the result of US air strikes on northern Syria, said Mr Lister. "An area like Homs is also a target that Isil would feel more comfortable with now, as the chance of air strikes hitting this area is less likely," he said. If the US government were to strike Isil targets around Homs, they would effectively be providing air support for the Syrian government - their declared enemy. The US - which has supported and armed the Syrian opposition - has denied that the air strikes it is conducting in Syria indicate a rapprochement with Mr Assad. The jihadist onslaught in Homs are also potentially incredibly damaging militarily for the Syrian regime. Both al-Sha'ar and Jahar gas fields were said to be being used as ad hoc military positions by the government, housing soldiers and stories weapons. The loss of Tayfur would be a major blow to Mr Assad, who, with his own army weakened, exhausted and underpaid, is, according to local reports, relying increasingly on Shia Muslim foreign militia fighters from Iraq, Iran, Lebanon and even Afghanistan. Bebar al-Telawy, an activist in Homs with extensive knowledge of the Syrian military's behaviour, said: "Tayfur airport is the front line of defence for regime loyalists. Planes fly from this base to bomb opposition held areas. Many massacres of civilians have started at this airport. Mr Lister said: "As far as I am aware the base is extremely active for launching air operations in the country." For the moment the Syrian regime appears to have resisted the onslaught, but it is unclear how many casualties it has incurred in that process. Video footage filmed by Isil fighters in al-Sha'ar showed the corpses of Syrian government fighters strewn on the ground. Mr Lister said a guess of between 25 and 50 dead was plausible. A change in the behaviour of the Syrian government on other front lines in Homs province, may indicate just how seriously the regime is taking the Isil threat. Activists in al-Waer, an opposition-held district of Homs that has been under siege by the Syrian government, told The Telegraph that the regime had been more open to negotiations since Isil attacked. Mr Telawy said: "The regime is trying to make a deal with the opposition to stand together if Isil advance further into Homs city. The request is that everyone fights Isil, whether the jihadists try to penetrate regime or opposition held areas. Isil briefly seized al-Sha'ar in July and lost it to the regime shortly after, but in that time the Syrian government had also made contact with al-Waer, Mr Telawy said. Last time Isil took over Sha'ar field, the regime started at that time to negotiate with al-Waer revolutionaries to reach a truce and to obtain a promise they would fight Isil if it attacked the Homs. Waleed al-Fares, a Syrian activist in al-Waer separately told The Telegraph that negotiations for a ceasefire were taking place.