British police said on Wednesday they had arrested two people at London's Heathrow Airport in connection with alleged terrorist acts in Syria.
A man and a woman, both aged 26, were detained by officers from the counter-terrorism command at 8.30 pm (1930 GMT) on Tuesday after arriving on a flight from Egypt, the Metropolitan Police said.
They were being held at a central London police station. Police searched two homes in east London in connection with the arrests.
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"The arrests form part of an investigation into travel to Syria in support of alleged terrorist activity," added the statement.
Foreign Secretary William Hague said that although he could not give more detail about the arrests, British authorities were keeping a close eye on foreigners seeking to join the fighting in the escalating conflict in Syria.
"We've had reports of course of foreign fighters, including British people, going to Syria," he told BBC TV.
"That's not something that we recommend and we do not want British people going and taking part in violent situations anywhere in the world, but I can't tell you more about those specific cases."