Second man arrested over London Underground bombing claimed by IS

A second man has been arrested over Friday's bomb attack on a London underground train that injured 30 people, police said on Sunday, as Britain remained on its highest level of alert with soldiers helping provide security.

The 21-year-old man was detained under Britain's Terrorism Act in the west London suburb of Hounslow just before midnight on Saturday, the Metropolitan Police said in a statement.

The arrest came as Home Secretary Amber Rudd repeated the British government's line that a claim US President Donald Trump that the culprits behind a bombing on a London train were in the sights of the police, made on Twitter shortly after the attack, had been nothing more than speculation.

“It's never helpful to have speculation about an ongoing operation and I would include the president of the United States in that comment,” Amber Rudd told BBC television on Sunday. “It is pure speculation, absolutely.”

Not helpful for anyone

Rudd's comments echoed those of British Prime Minister Theresa May who said on Friday it was not helpful for anyone to speculate on investigations.

Rudd added that police had made “very good progress” in their investigations,

On Saturday, police made their first arrest in the investigation when they took an 18-year-old man into custody in the port of Dover. Police then raided a property in Sunbury, a town near London and about four miles from Hounslow.

Local residents quoted in British media said the owners of the house were elderly foster parents, who were known for fostering hundreds of children, including refugees.

Ronald Jones, 88, and Penelope Jones, 71 were rewarded for their service to children when they were made MBEs in 2010.

The home-made bomb shot flames through a train carriage packed with commuters at west London's Parsons Green Tube station but apparently failed to detonate fully.

The Islamic State (IS) group claimed responsibility as it has for other attacks in Britain this year, including two in London and one at a concert by American singer Ariana Grande in Manchester in May.

Intelligence officials say there is scant evidence the militant group was behind the attacks.

Reduced threat level

Prime Minister Theresa May put Britain on its highest security level of “critical” late on Friday, meaning another attack might be imminent.

Soldiers were deployed to strategic locations such as nuclear power plants to release arms police for other duties, including increased patrols on public transport and at key sites.

However, the threat level was reduced on Sunday afternoon after the two arrests.

The first man arrested on Saturday was detained in the departure lounge of the port of Dover in what police said was a “very significant” step.