Bomb disposal squad stand in the street near Parsons Green tube station in London
Bomb disposal squad stand in the street near Parsons Green tube station in LondonReuters

British Police on Tuesday arrested a third man in connection with the terror attack on the London Underground last week, the Press Association reports.

The 25-year-old was held in a counter-terrorism raid in Newport, south Wales, shortly after 7:00 p.m. on Tuesday, according to the report.

The Metropolitan Police confirmed the arrest and also said a building in the town was being searched.

Two other men, aged 18 and 21, remain in custody in connection with Friday’s bomb attack on the Parsons Green station in south-west London.

The 18-year-old suspect was arrested in Dover on Saturday, while the 21-year-old man was detained in Hounslow, on the western rim of the capital.

The bomb went off during Friday's morning rush hour in a packed carriage and although the device is thought to have malfunctioned, it still wounded 30 people.

It was Britain's fifth terror attack in six months.

The Islamic State (ISIS) group claimed responsibility for Friday's explosion, though interior minister Amber Rudd voiced doubt over that claim.

"It is inevitable that so-called Islamic State or Daesh will try to claim responsibility but we have no evidence to suggest that yet," she told the BBC on Sunday.

On Sunday, after the arrest of the second suspect, Britain downgraded the nation's terrorism threat from critical to severe.

A critical threat level means another attack is "expected imminently" while a severe threat indicates an assault is highly likely.