In a joint statement, 13 rebel groups led by the al-Qaeda-linked Nusra Front slammed the Turkey-based Syrian National Coalition, saying it no longer represents their interests.

Several Syrian rebel groups, including a powerful al-Qaeda-linked faction, said on Wednesday they reject the authority of the Western-backed opposition coalition, as U.N. inspectors returned to the country to continue their probe into chemical weapons attacks.

In a joint statement, 13 rebel groups led by the al-Qaeda-linked Nusra Front slammed the Turkey-based Syrian National Coalition, saying it no longer represents their interests.

The statement reflects the lack of unity between the political opposition, based in exile, and the disparate rebel groups fighting President Bashar Assad’s regime in Syria’s civil war, which has killed over 100,000 people so far. It also highlights the growing irrelevance of the Coalition and its military arm headed by Gen. Salim Idris, who heads the Supreme Military Council supported by the West, amid increasing radicalisation on the ground in Syria.

The rebel groups’ statement called on all those trying to topple Mr. Assad’s government to unite under a “clear Islamic framework” an apparent reference to the al-Qaeda faction’s aspirations to create an Islamic state in Syria.

It said the rebels do “not recognise” any future government formed outside Syria, insisting that forces fighting on the ground should be represented by “those who suffered and took part in the sacrifices.”

But the rebels themselves are also deeply divided, with many groups blaming jihadis and al-Qaeda militants in their ranks for the West’s reluctance to intervene militarily in Syria or give them the advanced weapons they need. There is also growing concern that the dominant role the extremists are playing is discrediting the rebellion.

Yet the jihadis, including members of the Islamic State of Iraq and the Levant, an al-Qaeda offshoot, have been some of the most effective forces on the battlefield, fighting alongside the Western-backed Free Syrian Army to capture military facilities, strategic installations and key neighbourhoods in cities such as Aleppo and Homs.

Meanwhile, a team of U.N. chemical weapons inspectors arrived in Damascus on Wednesday to continue investigating what officials from the world organisation have described as “pending credible allegations” of the use of chemical weapons in Syria’s civil war.

The visit of the six-member team, led by Swedish expert Ake Sellstrom, follows a report by the inspectors after their previous trip in September, which said nerve agent sarin was used in an August 21, 2013 attack near the capital, Damascus.

The U.S. and its allies say Mr. Assad’s regime was behind the attack, and Washington said it killed 1,400 people. Syrian activist groups gave significantly lower death tolls, but still in the hundreds.

Damascus blames the rebels for the attack, and Russia, a close ally of Mr. Assad, said the U.N. report did not provide enough evidence to blame the Syrian government. It has also demanded that U.N. inspectors probe other attacks that allegedly included chemical agents.

The United States and Russia brokered an agreement for Syria to give up its chemical weapons but U.N. diplomats say they are at odds on details of a Security Council resolution spelling out how it should be done and the possible consequences if Syria doesn’t comply.

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