LONDON -- British police arrested two more men early Wednesday morning in connection with the bomb that partially exploded on a London subway last week. The new arrests, both in Wales, bring the total number of people held in the case to five, after a 25-year-old man was arrested Tuesday.

London's Metropolitan Police said in a statement on Wednesday that the fourth and fifth arrests in the case were made at about 5 a.m. local time (midnight Eastern) in Newport, South Wales, about 140 miles west of London.

Counter-terrorism officers executed a warrant at an address in Newport and took two men, 48 and 30-years-old, into custody.

Officers were still searching that address later Wednesday, in addition to the other property in Newport where the 25-year-old man was detained on Tuesday.

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Two other men arrested over the weekend -- an 18-year-old refugee from Iraq and a 21-year-old from Syria -- remain in custody. None of the men in custody had been charged as of Wednesday morning. London police have not released details from the investigation.

Commander Dean Haydon, head of the Metropolitan Police Counter-Terrorism Command, said searches were underway at four different locations, including three that were in progress before Tuesday. The searches may take "some days to complete" as detectives seek to determine the "full facts" behind the attack, Haydon said.

He asked the public to "look out for anything that seems out of place, unusual, or just doesn't seem to fit in with day-to-day life" and to notify police immediately if something seems amiss.

The homemade explosive device, which had been placed inside a bucket that was enclosed by a shopping bag, injured 30 people when it partially detonated inside a crowded subway car on Friday morning.

The subway was stopped at the Parsons Green station when the device went off.

Home Secretary Amber Rudd said the rush-hour explosion would have caused many more injuries if it had fully detonated.

Britain's official terrorist threat level was raised to "critical" after the attack - meaning an attack was judged to be imminent - but it was lowered after the first two arrests.

Those suspects are believed to have at one point lived in a foster home in Sunbury, a suburb southwest of London. Details about the third suspect have not yet emerged.

Islamic State extremists have claimed responsibility but British officials have said they don't see proof of a connection yet.