Al-Qaeda-linked gunmen killed a rebel commander in a coastal province in north-western Syria, an activist group said on Friday, a sign of increased tensions and infighting among Opposition groups battling the Damascus regime.

The Britain-based Syrian Observatory for Human Rights said members of the Islamic State of Iraq and the Levant, a reportedly merged group made up of al-Qaeda’s branches in Iraq and Syria were behind the shooting of the Free Syrian Army commander, Kamal Hamami.

The incident came as Syria’s main Opposition bloc complained that “elements in the U.S. Congress” are obstructing the Obama administration’s efforts to step up support for the rebels fighting to topple President Bashar Assad’s regime from power.

The Observatory said Hamami was shot dead late on Thursday after militants tried to remove a checkpoint he set up in the Jabal al-Akrad mountain in the coastal province of Latakia. It said two of his men were seriously wounded in the shooting.

Activists have in the past reported occasional clashes between rebel groups and Islamic militants active in rebel-held areas, especially in the north where the Opposition has control of a large part of the territory.

There has also been infighting between Kurdish and Arab groups over control of territory captured from the Government along the border with Turkey in the past year. That fighting subsided after a cease-fire agreement early this year.

The Free Syrian Army representatives could not be reached to confirm Hamami’s death.

Syria’s main rebel units, known as the Free Syrian Army or FSA, regrouped in December under a unified rebel command called the Supreme Military Council, following promises of more military assistance once a central council was in place. The Western-backed council is headed by Gen. Salim Idriss, who defected from the Syrian army, and a 30-member group of senior officers. Idriss spent 35 years in the Syrian military and is seen as a secular-minded moderate.

Some FSA units still operate autonomously, however, often fighting alongside more effective groups on the battlefield, including the al-Qaeda-affiliated Jabhat al-Nusra, which has led most successful battles for army bases, villages and towns in the north along the border with Turkey.

The group, known in English as The Nusra Front, has claimed responsibility for several car bombs and suicide attacks on military installations and government buildings, including in the capital Damascus, the seat of Assad’s power.

In a statement late Thursday, the Western-backed Syrian National Coalition urged Congress to back arms deliveries to the rebels.

President Barack Obama recently said the U.S. is willing to send weapons to the Opposition. Even so, Washington has been reluctant to arm the rebels battling Assad’s troops because radical Islamic groups, including some with al-Qaeda links, have emerged as their most effective fighting force. Western countries have also been concerned over the lack of unified command among rebel groups.

“The Syrian Coalition is deeply concerned by reports indicating that elements in the U.S. Congress are delaying the administration’s efforts to increase its support to the Free Syrian Army” said the statement late on Thursday.

The coalition will ensure “that arms will not reach extremist elements,” it added.

More than 93,000 people have been killed in the Syrian conflict that erupted in March 2011 with largely peaceful protests against Assad’s rule but escalated into a civil war in response to a brutal government crackdown.

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