The British police suspect that a fifth bomber was involved in last week's attempted suicide attacks at underground trains and a bus in London [Images], believed to have been carried out by four men, a report said on Monday.

With the discovery of a suspect package, appeared to be packed with explosives, nails and bolts, in northwest London on Saturday morning, police now fear that a fifth bomber was at large, The Times reported.

• London: Police carry out controlled explosions of suspected package

The police on Sunday carried out a series of controlled explosions to neutralise the package, which was found in some bushes in the Little Wormwood Scrubs neighbourhood.

Three men have been arrested so far under Britain's anti-terrorism laws in connection with the failed attacks on
July 21, but police have not released the details of any of them.

Police have also released images of the four suspected bombers captured by security cameras installed at underground train stations and at other places.

The report said the suspected bombers were believed to be of East African origin and none of them were in touch with their families after the incident.

"These men seem determined to die. They are likely to have been picked for their stronger resolve than the four men who died on July 7" after triggering blasts, killing 56 people, it said quoting an unnamed police source.

Meanwhile, investigators are also trying to identify the chemical signature of the explosive left in the rucksacks and match it to the bombs used on July 7, it said.

Also Read: The London Blasts