LONDON — Police arrested a 24-year-old man at London's Heathrow airport on Monday as part of an investigation into people traveling to Syria for "alleged terrorist activity."

The man, who had arrived in Britain on a plane from Bahrain, was held "on suspicion of the commission, preparation or instigation of acts of terrorism," said the force.

He was taken to a police station in south London for questioning by officers from Counter Terrorism Command, the police added in a statement.

Al-Qaida leader Ayman al-Zawahri last month called on Muslims to join the rebellion against Syrian President Bashar al-Assad, according to the SITE monitoring service.

Islamist militant groups have played an increasingly significant role in the fighting.

British police arrested a man and a woman at Heathrow last month as part of similar investigations into travel to Syria .

A 26-year-old man was charged on Oct. 16. The woman was released without charge.