British Home Secretary Charles Clarke said Tuesday there was likely a link between the bombers who carried out the July 7 London attacks and the group behind the failed July 21 bombings.
But Clarke said there was no evidence connecting the two groups of attackers, and added that investigators had yet to uncover any international links.
Fifty-two commuters died when four suicide bombers blew themselves up on three London subway trains and a bus on July 7. Three weeks later, four people failed to fully detonate devices on similar targets. The four men alleged to have carried out those attacks are in custody - three in Britain and one in Italy.
"I think it would be very, very surprising if they weren't linked in some way," Clarke said of the attacks in an interview with British Broadcasting Corp. radio, before adding: "There is not a direct linkage yet formally established."
Clarke also said investigators were trying to determine if the attackers received support or training from outside groups, and suggested they may have been part of a wider network. But he added: "The full international links in relation to all this still remain to be fully clarified."
Police have not charged anyone in the July 7 bombings. Three of the alleged July 21 attackers have been charged in Britain with attempted murder.
The fourth suspected July 21 attacker, Hamdi Issac, is in custody in Italy. Issac, 27, also known as Osman Hussain, was due to appear in court in Rome on Wednesday where Britain will press for Italy to extradite him, said Paolo Iorio, a lawyer representing the British government.
Clarke congratulated British police on the work they have done investigating the attacks, but acknowledged that police and security services had lacked prior intelligence about the strikes.
"There are a lot of people who believe that we know what is going on and simply aren't acting effectively enough to deal with it," he said. "The fact is we did not know of these proposed attacks and that has been the very striking fact of what has taken place."
Britain has announced a range of anti-terrorism measures since the attacks, including closing mosques linked with extremist clerics, and deporting or barring radical Islamic preachers from Britain. Last week, British authorities detained 10 foreigners, including radical preacher Abu Qatada, and aims to deport them in the interests of national security.
Clarke can deport or exclude people from the country if they threaten public order or national security and is trying to broaden the criteria for taking such action. After a two-week consultation period comes to a close on Friday, the government will have the power to act against anyone who foments, justifies or glorifies terrorism, fosters hatred or advocates violence, either through public speaking, preaching, running a Web site, or publishing leaflets.
In a statement, Clarke hinted that another group of foreign nationals could be taken into custody for possible deportation once the powers come into effect midnight Friday, the AP reports.
"We are continuing to look at people in this country whose presence here is not conducive to the public good," he said. "We will be looking at further steps that can be taken to ensure that those who are working against the interests of this country are properly dealt with."