Three men were arrested on Sunday at London's Heathrow Airport under anti-terrorism laws, a top British police official said.

"Three people have been arrested under the Prevention of Terror Act at Heathrow Airport but it is not known at this stage whether those arrests are linked to this inquiry or not," Scotland Yard Deputy Assistant Commissioner Brian Paddick said in a press conference.

Paddick said no link had been established between the arrests and last Thursday's four bombings on the London transport network, which killed at least 49 people.

"It is inappropriate and pure speculation at this stage to be drawing any direct linkages with the attacks in London, and at this stage we are not in a position to give any further information." said Paddick.

Three of the four explosions went off within seconds or almost simultaneously in London Thursday, contrary to previous speculation of within minutes of each other or even longer, policesaid Saturday.

Timing devices were likely used to set off the three bombs thatcaused carnage in the London Underground system, according to police.

The Abu Hafs al-Masri Brigade has claimed responsibility for the attacks in the name of al-Qaida. The grouping also claimed responsibility for the Madrid bombings which left 191 people dead.