The UK has offered assistance with investigations into the disappearance of a Malaysian Airlines plane with 239 people on board, Foreign Secretary William Hague said.
Mr Hague said it was "too early to speculate" on the significance of the presence on the flight of up to four passengers with suspect identities.
An air and sea hunt for wreckage from the Boeing 777 is continuing after it vanished from radar screens in fine weather en route from Kuala Lumpur to Beijing early yesterday morning.
No distress signal was sent by the pilots.
Among names on the flight manifest were those of an Italian and an Austrian - who were not on the flight but who had reported their passports stolen in Thailand, increasing fears of a terrorist connection.
"It is a terrible tragedy and our thoughts are with the families and loved ones of people awaiting for definitive news," Mr Hague told Sky News' Murnaghan programme.
"We have offered any assistance that we can give to the Malaysian authorities and of course we have been checking up on whether any British nationals were involved.
"We are not aware of any at the moment but we will continue that checking."
Asked about the significance of the suspect identities, he said: "It is too early to speculate about what that means.
"The UK will assist the Malaysian authorities in any way we can with any investigation if it is relevant to do so in any way."