LONDON: A second man has been arrested by police investigating Friday?s bomb attack on a London underground train, police said.

The 21-year-old man was arrested in the west London suburb of Hounslow just before midnight on Saturday, the Metropolitan Police force said in a statement.

He was detained under Britain?s Terrorism Act and taken to a south London police station, the force added on Sunday.

Earlier, police arrested an 18-year-old man in relation to the London train bombing that injured 30 people.

He was also arrested under the Terrorism Act in the southern port area of Dover.

Four previous attacks in London and Manchester this year claimed the lives of 35 people.

A home-made bomb on a packed rush-hour commuter train in London engulfed a carriage in flames and injured 29 people on Friday, but apparently failed to fully explode, in Britain?s fifth major terrorism incident this year.

Some suffered burns and others were injured in a stampede to escape the station ? one of the above-ground stops on the underground ?Tube? network ? but health officials said none were thought to be in a serious condition.