(Reuters) - British police said they have released two men arrested as part of the investigation into last week’s Tube attack in Parsons Green, London, which injured 30 people.

A 21-year-old man arrested in Hounslow on Sept. 16 and a 48-year-old man arrested in Newport on Sept. 20 were released by the police with no further action, the police said in a statement on late Thursday. bit.ly/2hnqiem

“We have four males in custody and searches are continuing at four addresses. Detectives are carrying out extensive inquiries to determine the full facts behind the attack,” the police said.

A home-made bomb went off on Sept. 15 during the morning rush hour on a packed underground Tube train at Parsons Green station, sending flames through the carriage, although it appeared that the device did not fully explode.

It was the fifth major militant incident in Britain this year.

The Islamic State militant group, which had said it was behind several attacks on Western cities in recent years, including two attacks in London and one in Manchester this year, claimed responsibility for the latest attack.