The US and Britain both announced Wednesday they would be cutting off nonlethal assistance to opposition groups fighting in Syria, even as UK Prime Minister David Cameron warned against the idea that all of Syria’s opposition is extremist.

His comments came as a US Embassy official in Turkey said the United States is suspending all nonlethal assistance destined for the opposition in northern Syria because of rebel infighting.

Washington’s decision came days after fighters from the Islamic Front, an umbrella group of six major rebel groups, seized bases and warehouses belonging to the mainstream Western-backed Free Syrian Army rebel group at the Bab al-Hawa crossing between Syria and Turkey.

The American official said humanitarian assistance would not be affected. He spoke on condition of anonymity because he was not authorized to release the information.

Britain’s Foreign Office said it is investigating those incidents and that it “will not be making any deliveries of equipment” to the Free Syrian Army while that investigation is under way.

It said it intends to resume assistance as soon as conditions on the ground allow for the “safe delivery” of equipment provided.

It was not clear why the Islamic Front seized the bases. The new alliance is independent from the FSA and seeks to establish an Islamic state in Syria.

Cameron told British lawmakers on Wednesday that Britain should be “fully engaged” in all efforts to end the civil war.

He said, “we must not allow this argument to develop that the only opposition in Syria is an extremist opposition,” because that will only become reality if “we stop working with those who care about democracy and the future.”