According to Zvi Bar'el the Israeli analyst writing in Haaretz 3rd June 2015 the "Assad regime forces abandoned the city of Palmyra and allowed ISIS to take it over unopposed, and it appears they may do the same in the southern province of Daraa, leaving ISIS to fight the other rebel groups on their behalf. Salim Idris, defense minister in the rebels' provisional government, said approximately 180 Syrian Army officers are currently serving with ISIS and coordinating the group's military operations with the army".
According to media reports in June 2014 the Assad regime had refrained from attacking ISIS bases. A Syrian government adviser told the New York Times' Anne Barnard this was indeed a deliberate policy designed to "tar" the broader opposition and "frame [the] choice" as either Assad or the extremists.
In a further twist that implicates the Assad regime in collusion with ISIS, on 6th February 2015 the US Embassy in Syria accused the regime of supporting ISIS advance on Syria's largest city, Aleppo. The Embassy tweeted:
"Reports indicate that the regime is making air-strikes in support of ISIL's advance on Aleppo, aiding extremists against Syrian population," said the post.
In a string of tweets, the U.S. embassy condemned Assad's actions, saying he "will never be an effective counterterrorism partner." Embassy operations have been suspended since 2012, but the Twitter account is still active.
In March 2014 the news media reported that the EU issued sanctions against "seven persons and six entities providing support to the Syrian regime as well as benefitting from it". They included George Haswani, a prominent Syrian businessman said to be in direct contact with Assad and accused of brokering oil deals between the regime and ISIS.
The sanctions against Haswani represent one of the first official positions taken by Western countries acknowledging the links between the terror group and the Syrian regime, a position long maintained by those in the region and beyond.
Philip Hammond UK Foreign Secretary announced at the time:
"We have also agreed to target individuals supplying oil to the regime, including George Haswani, a middleman buying oil from ISIL [Isis] on behalf of the regime. This listing gives yet another indication that Assad's 'war' on ISIL is a sham and that he supports them financially."
In January 2014 a report in the Daily Telegraph by Ruth Sherlock drew attention to the oil deals between ISIS and the Assad regime.
"The regime has "financed" the jihadists "by selling oil and gas from wells under their control to and through the regime".
The Iranian Link:
A question that puzzled Western observers what would Iran's motivation be to support a Sunni jihadist organizations like ISIS? In Syria, ISIS has forced the West to choose between the regime of Bashar al-Assad or a terrorist outfit. Given that choice, it was assumed that the West would back Assad, as did the Russians and the Chinese.
Cynically Iran is exploiting the Western fear of terrorism to make common cause with the West against ISIS.
But ample evidence exists to prove Iran's collusion with Al Qaeda. The US 9/11 Commission Report, had already established that Iran "facilitated the transit of Al-Qaeda members into and out of Afghanistan before 9/11, including future hijackers. Iran, according to the report, wished to conceal any past evidence of its cooperation with Sunni terrorists' association with Al-Qaeda," but these connections continued.
At ISIL's headquarters in rural western Aleppo in March 2014 opposition forces discovered official documents, passports and SIM cards issued by the Iranian authorities to fighters from Chechnya and Kazakhstan. Doesn't this suggest some kind of connection between ISIL leaders and Iranian intelligence, of which rank and file of ISIS are likely ignorant?
ISIS suddenly emerged in Syria, at a time when the collapse of Assad's regime seemed imminent. The emergence of ISIS saved the Syrian regime by threatening the world that an alternative terrorist regime would replace Assad's.
A report in the Economist magazine 21st June 14 explained how ISIS was less interested in toppling the Assad's regime than fighting other groups.
ISIS has been criticized for its attacks on civilians and rival opposition groups. It has rarely targeted the Assad's regime and not a single barrel bomb has been dropped by the regime on ISIS.
Iran actually has a lot to gain from keeping ISIS alive. As long as the group survives, Iran can claim that their allies in Syria and Iraq are preventing a jihadist takeover -- an argument that raises Tehran's prestige and ensures it a degree of international support for their allies in both countries. This argument has so far worked. The Guardian reported in Sept 2014 that "the Syrian government and its close allies in Moscow and Tehran warned Barack Obama that an offensive against Islamic State (Isis) within Syria would violate international law". The implication is obvious: leave ISIS alone.