LONDON, Sept. 17 (Xinhua) -- The United Kingdom maintained the highest terrorism threat level in London and other parts of the country on Sunday after a second man was arrested in connection with the Friday explosion in a packed rush-hour carriage at a subway station in the western part of the British capital.
The 21-year-old man was arrested in Hounslow around 11:50 p.m. BST on Saturday under the Terrorism Act, police said early Sunday. He was taken to a south London police station and remains in custody.
The latest arrest was made after London's Deputy Assistant Police Commissioner Neil Basu said police were keeping an "open mind" over whether more than one suspect was involved in the bombing.
Basu, who described the arrest as "very significant," said, "If there are other people responsible it's our job to find them and that is part of the reason that we are remaining at critical threat."
The British raised the terrorism threat level from "severe" to "critical" just hours after the explosion, which was caused by an improvised explosive device.
The "critical," the highest of the five levels used to describe the threat, means a further terrorist attack may be imminent.
Thirty people were injured, none of them seriously, after the explosion took place at Parsons Green subway station in west London on Friday, prompting the police to stage a massive hunt for those who are responsible for the fifth terrorist attack in the country over the past six months.
Previous attacks in London this year at Westminster Bridge, London Bridge and Finsbury Park as well as a blast at an Ariana Grande concert in Manchester killed dozens of people and injured more than 150.
The Islamic State has claimed responsibility for the Friday subway explosion.
At least 1,000 armed police are patrolling streets in London, and the military forces are mobilized to protect strategic points across the country.
British Home Secretary Amber Rudd said on Sunday that an extra of 24 million pounds (about 32 million U.S. dollars) is to be pumped into counter-terrorism policing in the wake of this year's terror attacks.
The extra funding will go to counter-terrorism police including the police forces in London and Manchester to assist with their response to the threat of terrorism and help meet costs relating to the recent terrorist attacks.
"The threat we face from terrorism is becoming more complex and diverse," Rudd said in a statement. "That is why we are reviewing our counter-terrorism strategy to ensure the authorities have the powers they need to halt terrorist activity and why, today, I have announced 24 million pounds of additional support for counter-terrorism policing this year."
The new government move came as the investigation into the subway blast is underway.
Armed police launched a raid on a property in Sunbury-on-Thames, Surrey following the arrest of the 21-year-old man.
As many as 60 homes in the area were evacuated "as a precaution."
At present, British police are raiding a home in Stanwell, about 25 kilometres southwest of central London, linked to the arrest of the second suspect.
Experts said the bomb, which was placed in a bucket and concealed in a plastic bag, could have been far more destructive if it had fully detonated.
Two days after the attack, all but one of the people injured had been released from hospital, the British National Health Service said.
One person was still being treated at Chelsea and Westminster Hospital, which has a special unit for treating burns.
