The U.S. suspended delivery of nonlethal aid to Syrian rebels in the northern part of the country after an Islamist group seized warehouses belonging to the Western-aligned Free Syrian Army, raising doubts about the influence of moderate rebels in the nation’s increasingly factional war against government forces.

U.S. humanitarian aid to Syria remains unaffected, the State Department said, and so does a program to supply light weaponry to rebels in southern Syria, the Washington Post, citing officials, reported. The UK joined the U.S. in suspending delivery of nonlethal aid in response to the seizure, but humanitarian assistance will continue, UK Foreign Office Minister Hugh Robertson told the BBC.

The Islamic Front, which has taken control of the warehouses, is an alliance of seven leading rebel groups with an estimated 45,000 fighters who say they don't have ties with al Qaeda or its affiliates such as the Jabhat al-Nusra, an Islamist radical group blacklisted by the State Department as a terrorist organization.

The Islamic Front announced its withdrawal from the FSA’s Supreme Military Council last week and then proceeded to capture SMC’s bases and warehouses at Bab al-Hawa, in the northwestern province of Idlib.

“The headquarters and warehouses belonging to the SMC have been taken over is certainly something concerning and has left us to … suspend all deliveries at this point,” State Department spokeswoman Jen Psaki said in a press briefing in Washington,  adding that the decision to suspend aid delivery does not imply any changes to U.S. policy on supporting the SMC's forces.

“This has nothing to do with our support for the SMC. It has nothing to do with our support for the opposition. It has everything to do with the security of the material assistance, which is, of course, what we’re evaluating,” Psaki said. “The SMC continues to be – and this has not changed – the group that we work through and that we want other countries to provide aid and assistance to.”

The Syrian Observatory of Human Rights, a UK-based rights group, said arms, including antiaircraft weapons and antitank rockets, have been captured by the Islamic Front, but Psaki said the department’s “understanding at this point” is that only nonlethal aid such as ready-to-eat food kits and laptops among other things were at the warehouse at the time of the seizure, and that the state department is evaluating the presence of any weaponry.

Meanwhile, the FSA expressed disappointment over the suspension of deliveries, saying: “We hope our friends will rethink and wait for a few days when things will be clearer,” spokesman Louay Meqdad was quoted as saying by Reuters.