On Sunday, Taliban commanders in Pakistan said they had also decided to join the cause, saying hundreds of fighters had gone to Syria to fight alongside their “Mujahedeen friends”.

“When our brothers needed our help, we sent hundreds of fighters along with our Arab friends,” one senior commander told Reuters, adding that the group would soon issue videos of what he described as their victories in Syria.

The announcement further complicates the picture on the ground in Syria, where rivalries have already been on the boil between the Free Syrian Army and the Islamists.

Islamists operate a smaller, more effective force which now controls most of the rebel-held parts of northern Syria. Tensions erupted again on Thursday when an al-Qaeda linked militant group assassinated one of Free Syrian Army’s top commanders after a dispute in the port city of Latakia.