LONDON (AP) -- British police searched two east London properties Wednesday as part of the investigation into the activities of a man and a woman arrested on suspicion of supporting terrorism offenses in Syria.
Police took the pair, both aged 26, into custody late Tuesday, after they flew into Heathrow Airport from Egypt. Police provided few details.
Most of those fighting the regime of President Bashar Assad are believed to be ordinary Syrians and soldiers who have defected, having become fed up with the authoritarian government, analysts say. But increasingly, foreign fighters and those adhering to an extremist Islamist ideology are turning up on the front lines.
The rebels are trying to play down their influence for fear of alienating Western support, but as the civil war grinds on, the influence of these extremists is set to grow.
The Syrian government has always blamed the uprising on foreign terrorists, despite months of peaceful protests by ordinary citizens that only turned violent after repeated attacks by security forces. The transformation of the conflict into an open war has given an opening to the foreign fighters and extremists.
Talk about the role of foreign jihadists in the Syrian civil war began in earnest, however, with the rise in suicide bombings. U.S. National Director of Intelligence James Clapper said in February that those attacks "bore the earmarks" of the jihadists in neighboring Iraq.
Rebel commanders are quick to dismiss the role of the foreign fighters and religious extremists, describing their numbers as few and their contribution as paltry.
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 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.
Britain's Foreign Secretary William Hague warned Britons against traveling to Syria to take part in the fight to depose Assad. Hague told the BBC that the government is aware of some Britons joining the pitched battles for control of Syria.
"That's not something we recommend, and we do not want British people taking part in violent situations anywhere in the world," he said.
Fears that British Muslims might be slipping into Syria to join 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.
The British police statement said the man and woman 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.
Elizabeth A. Kennedy in Beirut and Raphael Satter in London contributed.