British Prime Minister Tony Blair says there was no way anyone could have prevented last week's attacks, and he vowed to hunt down those responsible - both the perpetrators and the planners.

"We will pursue those responsible wherever they are and we will not rest until they are identified, and as far as possible, brought to justice," Blair told the British parliament.

"I know of no intelligence specific enough to have allowed them to prevent last Thursday's attacks. By their very nature, people callous enough to kill completely innocent civilians in this way are hard to stop," he said.

His comments came as the death toll rose to 52 from 49. Workers continue to pull corpses from a mangled Underground train.

Another 700 were injured in the attacks, and more than 20 remain missing.

Scotland Yard said Monday it had identified the first of the victims as Susan Levy, 53, of Hertfordshire, outside London.

University College London also confirmed that cleaner Gladys Wundowa, 51, died in the bus bombing in Tavistock Square, according to the website of the British Broadcasting Corporation.

Forensic experts warn it could take weeks to identify all the victims.

Security alerts

As the recovery effort continues, security scares are ongoing.

Police briefly closed an area of central London on Monday, including the street outside Parliament Square, after a suspicious package was found.

The package turned out to be harmless, but police were busy clearing the Whitehall area of most traffic and pedestrians, including many tourists. Sniffer dogs were also apparently brought in.

Police also issued a security alert at the King's Cross subway station near the site of one of last week's bombings. No explanation was given. BBC television said a suspicious package was also found there.

Meanwhile, transit officials said the number of passengers using the system Monday morning was back to normal. Some of the stations hit by the bombings remained closed.

Among those using the transit system today was London Mayor Ken Livingstone.

"We are going to work. We carry on our lives," he said. "We don't let a small group of terrorists change the way we live."

Military-type explosives?

There are reports that the type of explosives used in the bombings appears to be military.

Christophe Chaboud, the head of France's Co-ordination Anti-Terrorist Unit, visited London to meet with British anti-terrorism officials.

"The nature of the explosives appears to be military, which is very worrisome,'' Chaboud said in an interview published Monday with Le Monde.

"We're more used to (terror) cells making homemade explosives from chemical substances,'' he added.

He said there are only two ways to get such explosives -- either by trafficking or by stealing them from a military facility.

Blair said it seems probable the attacks were carried out by "Islamist al Qaeda extremist terrorists of the kind who over recent years have been responsible for so many innocent deaths."

However, the authorities still don't know exactly who was responsible.

Meanwhile, Britain's security alert remains at its highest level. No suspects have been captured yet in relation to the attack, leading to fears of a second series of bombings.

Early Sunday, British police arrested three men -- all Britons -- arriving at Heathrow airport. They were released late Sunday evening without charge, and police were quick to say the arrests did not stem from intelligence related to the bombings.

Olympics still a go

Thursday's bombing came one day after the International Olympic Committee announced that London had won the right to host the 2012 Summer Olympic Games.

On Monday, IOC President Jacques Rogge confirmed the Games would stay in London, despite the attacks.

"We trust the London organizers to secure the best possible security arrangements in 2012," Rogge said, adding that, "no city in the world can claim that nothing will happen in each city."