The US and UK have decided to suspend all “non-lethal assistance” for Syrian rebels.

A US embassy spokesman in Ankara said the decision was made after Islamist rebels seized bases belonging to the Western-backed Free Syrian Army (FSA).

Fighters from the Islamic Front, a new alliance of major rebel groups, took control of the bases at the Bab al-Hawa border crossing with Turkey last week.

Humanitarian assistance by the US and UK is not expected to be affected.

That was distributed through international and non-governmental organizations, the US embassy spokesman added.

Last month, seven leading rebel groups – the Ahrar al-Sham, Jaysh al-Islam, Suqour al-Sham, Liwa al-Tawhid, Liwa al-Haqq, Ansar al-Sham and the Kurdish Islamic Front – declared that they were forming the largest alliance yet in the 33-month conflict, with an estimated 45,000 fighters.

Fighters from the Islamic Front, a new alliance of major rebel groups, took control of the bases at the Bab al-Hawa border crossing with Turkey

They said the new Islamic Front was an “independent political, military and social formation” that aimed to topple President Bashar al-Assad’s government and build an Islamic state.

The front does not include al-Qaeda affiliates like the Islamic State in Iraq and the Levant (ISIS) and the al-Nusra Front, but its charter welcomes “muhajirin”, or foreign fighters, as “brothers who supported us in jihad”, and suggests it is willing to co-operate with them.

Last week, the Islamic Front announced that it had withdrawn from the command of the FSA’s Supreme Military Council (SMC), which is aligned to the opposition National Coalition.

Four days later, its fighters drove out SMC-aligned forces out of their bases and warehouses at Bab al-Hawa, in the north-western province of Idlib, which contained weapons and equipment that had been brought into Syria through Turkey.

SMC spokesman Louay Meqdad said the Islamic Front had raised its flag in place of the SMC’s after “asking” its personnel to leave. But he also stressed: “We believe that those brigades are our brothers, that they know that we are not the enemy.”

On Wednesday, the US embassy spokesman told the Reuters news agency that the situation at Bab al-Hawa was being investigated to “inventory the status of US equipment and supplies provided to the SMC”.

The US government has committed to provide $250 million in non-lethal assistance to the National Coalition, local opposition councils and the SMC. Rebel brigades have been provided with food rations, medical supplies, communications equipment and vehicles.