LONDON, (Reuters) – British police have arrested a man and a woman at London’s Heathrow airport as part of an investigation into travel to Syria in support of “alleged terrorist activity”, police said in a statement on Wednesday.

The pair, both 26 years old, were arrested on Tuesday evening after arriving on a flight to Heathrow and taken to a police station in central London where they remain in custody.

Police did not disclose the nationality of the two suspects. A spokesman declined to say whether these were the first arrests in Britain connected to events in Syria.

The police statement said the pair were arrested “on suspicion of the commission, preparation or instigation of acts of terrorism”.

Police searched several residential addresses in east London in connection with the inquiry, which was continuing, the statement said.

Foreign Secretary William Hague, asked on BBC radio whether the arrests were evidence that there were people in Britain who wanted to join the fighting in Syria, said: “There is some evidence that yes, there are people who want to do that.

“We would strongly advise them not to do so, and while I can’t comment at the moment in further detail on these cases, 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.”

Hague said the government was advising British nationals in Syria to leave the country, and all others not to travel there.

“We don’t supply ourselves anything that could contribute to lethal action inside Syria and of course we don’t want individuals to do that either,” he said.