British police said Wednesday that they had arrested two people at London's Heathrow Airport as part of an investigation into travel to Syria in support of alleged terrorist activity.

Scotland Yard said in a statement released early Wednesday that counter-terrorism officers arrested a man and a woman, both 26, after they flew into the airport from Egypt late Tuesday.

Police did not make clear whether the suspects were thought to be returning from or heading to Syria. The statement said that officers were searching two homes in east London as part of the investigation.

The statement added that the pair were arrested on suspicion of the "commission, preparation or instigation of acts of terrorism." The statement did not include the suspects' names, nationalities, or any other identifying information. The suspects were taken to a central London police station and remain in custody.

A police spokesman said no further comment would be made until later Wednesday

The fear of terrorist activity in Syria has grown as the bloody civil war there grinds past the 18-month mark. A U.N. panel warned last month that the number of foreign fighters in the conflict was growing — a development which it said could radicalize the rebellion against President Bashar Assad's rule. The Quilliam Foundation, a London-based think tank studying extremism, estimated that there were a total of 1,200-1,500 foreign fighters across Syria.

Concerns are particularly acute in Britain, which is home to a large Muslim population and suffered a devastating 2005 terrorist attack perpetrated by British-born Islamists. Fears that British Muslims might be slipping into Syria to join al-Qaida extremists were heightened in August when freelance photographer John Cantlie claimed he had been held hostage by a group of extremists including a man he identified as having a London accent.