Two people have been arrested at Heathrow airport on suspicion of terrorism offences related to Syria.
A man and a woman were held at 8.30pm on Tuesday after arriving on a flight into the airport from Egypt, the Metropolitan police said.
The pair, both aged 26, were arrested by officers from the counter-terrorism command on suspicion of the commission, preparation or instigation of acts of terrorism.
They were taken to a central London police station where they were being held in custody.
Scotland Yard said in a statement released early Wednesday that the pair had flown into the airport from Egypt.
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 under the Terrorism Act 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" but did not release their names, nationalities, or any other identifying information.
The arrests were part of an investigation into travel to Syria in support of alleged terrorist activity, police said.
William Hague, the foreign secretary, said he could not comment on the specifics but added that Britons should not be in Syria or travelling to the country.
He said: "There is some evidence there are people [here who want to join the fighting]. We could strongly advise them not to do so.
"On the general subject we are clearly very vigilant about this, about people either passing through the UK or British nationals who want to commit acts of violence anywhere, we are always vigilant about that.
"But we also advise all British nationals to leave Syria, not to go to Syria, we don't supply ourselves anything that could contribute to lethal action inside Syria and we don't want individuals to do that either."
The nationalities of the arrested pair have not yet been released, but they are not Egyptian. The two addresses being searched in east London are residential, Scotland Yard said.