The militants of Islamic State have reportedly struck a deal with moderate Syrian rebels not to fight each other and focus on toppling the government. Some reports say the deal was brokered by the Al-Nusra Front, an Al-Qaeda branch in Syria.

The IS, formerly known as ISIS/ISIL, is preparing its forces in Syria for likely bombings by the US, which now considers itself at war with the extremist movement. In addition to spreading out from their known facilities, the group that took over portions of Syria and Iraq to build a caliphate is apparently seeking to safeguard itself from attacks of other armed groups in the war-torn country.

According to the Syrian Observatory for Human Rights, a London-based conflict watchdog, the IS has signed a non-aggression pact with moderate fighters, who control the Hajar al-Aswad neighborhood of Damascus.

Under the deal, "the two parties will respect a truce until a final solution is found and they promise not to attack each other because they consider the principal enemy to be the Nussayri regime," AFP reported. “Nussayri” is a derogatory name for the Shiite Alawite sect, to which Syrian President Bashar Assad and many of his officials belong.

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According to Orient Net, the truce is meant to stop fierce fighting that engulfed the neighborhood for over 40 days and was brokered by the Al-Nusra Front, an Al-Qaeda affiliate that has frequently clashed with the Islamic State, which itself splintered from the terrorist network to pursue an independent struggle for power in the region.

The moderate rebels who signed the deal include four distinct groups, including the US-backed Syria Revolutionary Front, reported Charles Lister, an analyst at the Brookings Institute. The SRF was considered moderate enough to merit the West’s support and a part of the Free Syrian Army, a loose coalition of secular and moderate groups fighting to topple the Assad government with the blessing of Washington.

In an earlier interview with the Independent, SRF leader Jamal Maarouf said that Al-Qaeda was not his problem and that he would welcome “anyone who fights against the regime inside Syria."

The news comes as the US Congress is considering a $500 million request from the Obama administration to train and arm moderate rebel groups in Syria. Washington refuses to send its own troops on the ground against the IS and will limit its military action to reconnaissance and airstrikes instead.

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This means that the shooting part of the war against the Islamists, which Obama declared, would have to be fought by forces like the Kurdish militia, which already receives arms from the US and some European countries, and moderate Syrian rebels. The reported alignment of supposedly moderate SRF with America’s enemies raises the question whether Washington would be able to vet the recipients of its military aid to ensure that those arms and training would not be eventually used against it.

The Obama administration seems to be confident of this.

"We have been working with the Syrian opposition now for a couple of years, providing them assistance, non-lethal at first but then we [now] provide them with some military assistance, so we know them better today than we did a year, two years ago," deputy national security adviser Ben Rhode told The Huffington Post before the news of the deal broke.

"If we were to try to run a play with Assad, we would ensure that they were turned against us, and in fact we would be taking sides in a sectarian war against one side,” he added.