London police say a second man has been arrested in connection with the London underground attack.
Police said today that a 21-year-old man was arrested late Saturday night (local time) in Hounslow in west London. He was arrested under the Terrorism Act.
Two men are now in custody for possible role in the attack that injured 29 people.
Police earlier arrested an 18-year-old man in the port of Dover, the main ferry link to France, and then launched a massive armed search in the southwestern London suburb of Sunbury in which they evacuated residents, established a huge cordon and imposed a no-fly zone above the property being searched.
Police did not say that they had nabbed the man believed to have planted the bomb that partially exploded on a crowded London subway train Friday morning (local time), but Home Secretary Amber Rudd and others said the arrest was of major importance.
The man is being held under the Terrorism Act and has been brought to London for questioning.
His identity is a closely guarded secret and police have implored the press not to speculate while the inquiry unfolds. Authorities would not say if they thought the man was trying to flee to France on a Dover ferry.
Hundreds of soldiers patrolled public areas Saturday (local time), freeing up police for the bombing investigation.
Rudd said the country's terror threat level, which was raised Friday night (local time) to the highest possible level, will stay there until the independent Joint Terrorism Analysis Centre is convinced the threat of imminent attack has eased.
The homemade bomb on the rush-hour train only partially detonated, Rudd said it could have been much worse, and there are fears that accomplices may have similar devices.
Experts said the bomb could have caused many fatalities if it had functioned properly. Three of the 29 people injured by the blast remained hospitalised Saturday (local time).
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