"I'm confident, absolutely confident, that in the coming days and weeks we will be able to gain a thorough understanding of the methods used by the terrorists, the way in which they planned their attacks and the network to which they belong," he said.
The attacks led to the government raising the security alert level for the country to "critical", the highest on a five-level scale.
But on Monday, British newspapers argued against the government rushing through new "anti-terrorism" legislation.
The Daily Telegraph said in an editorial: "The immediate aftermath of a terrorist atrocity is the worst possible time to legislate.
"The government's response to the bombers should be proportionate to the threat faced, not to the public outrage."
The Independent took a similar line saying it "is vital that the prime minister does not rush through new repressive anti-terror laws ... it is vital that our political leaders pause for thought".
The Labour government of Tony Blair, the former prime minister, tried to push through new laws after the 2005 London transport system bombings that killed 52 people.
The bill, which would have let police detain suspects for 90 days without charge, was defeated.
Gordon Brown, the new prime minister who replaced Blair on Wednesday, said before taking office last week that he wanted police to have the extended detention rights.
|Properties in Glasgow, Liverpool and central |
England were searched on Sunday [AFP]
The Daily Mail
, a newspaper that is often critical of the governing Labour Party, offered tentative praise for Brown and Jacqui Smith, the new interior minister.
"This time ... there has been no political grandstanding, no promises of 'tough' new measures. Instead, Gordon Brown and Jacqui Smith concentrate on reassuring the public and letting police and MI5 [the domestic intelligence service] get on with the job. And that is surely right," it said.
Police confirmed on Sunday that one man and one woman arrested on a motorway near Liverpool were being interviewed in London.
They also said that a controlled explosion had been carried out on a car outside a hospital where one of the Glasgow suspects is being treated for burns.
A British government security official told the Associated Press that a loose UK-wide network appeared to be behind the attacks but investigators were struggling to ascertain suspects' identities.
"These are not the type of people who always carry identity documents, or who use their real identities," the official said on condition of anonymity.
Residents of homes near addresses being raided by police officers in central England and Liverpool said the residents were doctors or medical students. Police in London and Glasgow refused to comment on the claim.
The United States increased security at airports following the attempted attacks in Britain, while Michael Chertoff, homeland security secretary, said that more air marshals were being deployed on flights to Britain.
George Bush, the US president, praised Brown's "very strong response" to the situation during during a visit by Vladimir Putin, the Russian president.
In Paris, Michele Alliot-Marie, French interior minister, called a meeting with security chiefs to discuss events in Britain, while Ban Ki-moon, the UN secretary general, said "no cause or belief can justify such acts of terrorism".