London's top policeman has said the attempted bombings in the capital were designed to kill.

But Ian Blair added that evidence left at the scenes could be very helpful.

London mayor Ken Livingstone - who said this week that Western foreign policy has contributed to the spread of extremist beliefs - said Londoners will "get through this".

"It is not surprising that we have had another attempt to take life in London so rapidly after the first. Those whose memories stretch back to the terrorist campaigns of the 70s, 80s and early 90s will remember that, very often, horrifying bombings in London happened only weeks apart," he said.

Mr Blair said: "There is a resonance here. These are four attacks, there were four attacks before. Whether or not this is directly connected, in the sense of being carried out by the same group of people, however loosely knit that group is - I think that's going to take just a little longer before we can qualify that."

There has been speculation that the devices used were so similar to those used two weeks ago that they may even have been part of the same batch.

No London attack suspects arrested in Pakistan: diplomat

Britain has said none of those arrested in recent raids in Pakistan were suspects in the July 7 London bombings.

In a speech the UK's senior diplomat in Pakistan, Mark Lyall Grant, contradicted media reports to that effect.

"These attacks were not carried out by foreign states, they were carried out by British individuals. And let me take this opportunity to clarify that there have not been any arrests in Pakistan since 7 July related to the London bombings," he said.

In the past week Pakistani security forces have detained around 300 people suspected of involvement in Islamic extremism.

In a televised address President Pervez Musharaff said Pakistan had a problem with terrorism within its borders but added that Britain faced similar challenges.

He pointed out that while three of the suspected London bombers were of Pakistani descent they were born and brought up in the UK.

Musharaff also announced new tighter controls on some Islamic religious schools which authorities fear may be recruiting grounds for extremist organisations.

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