British police arrested a man and a woman at London's Heathrow Airport as part of an probe into people traveling to Syria participate in alleged terror activities.
The suspects, both 26, were arrested Tuesday night after arriving on a flight from Egypt, London's Metropolitan Police said in a statement.
The statement did not say whether the suspects were headed to Syria or had returned from there. Authorities did not release their names.
The pair were taken to a central London police station and authorities began searches of two homes in east London as part of the investigation, police said.
The UK Foreign Office did not want to comment directly on the arrests but said the "deteriorating security situation (in Syria) leaves dangerous space for foreign fighters."
"We are concerned about reports of extremist groups operating in Syria and we take very seriously any claims that British nationals are among foreign fighters there," the Foreign Office statement added.
The two people arrested at Heathrow are both British nationals, according to police sources.
One line of inquiry being followed by investigators, the police sources said, is whether the two suspects were involved in an incident in July in which Sunday Times photographer John Cantlie said he was held at gunpoint by rebels in Syria.
Some of those who detained him spoke with an English accent, Cantlie said.
The photographer declined to comment on the arrests or the incident in Syria when contacted by CNN Wednesday.