LONDON (AFP) -A defiant Prime Minister Tony Blair vowed that Britain would not be defeated by terrorists as he fended off calls for an inquiry into whether intelligence services could have averted bombings that killed at least 52 people.

In a statement to a hushed House of Commons, Blair praised the &#34stoicism, resilience and sheer undaunted spirit&#34 of Londoners, who returned to work Monday on buses and trains after being shaken by last week”s attacks on the capital”s public transport system.

&#34We are united in our determination that our country will not be defeated by such terror,&#34 Blair said.

As the confirmed death toll from Thursday”s attacks rose to 52, the tragedy took on a more individual face with the formal identification of the first two victims.

In his statement, Blair confirmed that three of the bombs, all on subway trains, had gone off within 50 seconds at the peak of Thursday morning”s rush hour, and that their timing was designed to cause &#34maximum death and injury&#34.

The fourth bomb went off just under an hour later on a double-decker bus.

It was &#34probable&#34 that the bombs were planted by &#34Islamist extremist terrorists&#34 of the kind responsible for outrages such as the September 11 attacks in the United States and those in Madrid in March 2004, Blair said.

The prime minister said he knew of no intelligence that would have allowed the police and intelligence services to prevent the atrocities, the deadliest attacks on British soil since World War II.

Blair rejected a call for an inquiry into the effectiveness of the intelligence services proposed by Michael Howard, leader of the main opposition Conservative party.

Security forces would be too busy investigating the attacks to deal with such a probe, the prime minister argued.

The intensive police operation now under way to find the bombers and bring them to justice was &#34among the most vigorous and intensive this country has ever seen,&#34 Blair said.

&#34We will pursue those responsible — not just the perpetrators but the planners of this outrage — wherever they are and we will not rest until they are identified and as far as is humanly possible brought to justice,&#34

According to a report in Tuesday”s edition of The Times newspaper, similar components were found by police at all four bomb sites, meaning all the devices were likely to have been produced by the same bomb maker.

Investigators believe the rucksack-based bombs were manufactured using smuggled, military-grade explosives, possibly brought in from the Balkans, the paper added.

The first two confirmed victims were named as Susan Levy, a 53-year-old mother of two from Hertfordshire, north of London, and Gladys Wundowa, 51, who worked for University College London as a cleaner.

Levy is believed to have died in the deadliest single blast, on a subway train travelling between the central London stations of King”s Cross and Russell Square, while Wundowa was killed on the bus.

Earlier Monday, London Mayor Ken Livingstone rallied the city”s people to overcome their fears and use public transport as they returned to work.

&#34We don”t let a small group of terrorists change the way we live,&#34 Livingstone said as he boarded a subway train for his own office.

Transport for London officials anticipated that fewer people would use trains and buses on Monday either because of security fears or disruptions to lines, but expected a normal passenger load to return over the next few days.

Police said one London Underground line remained suspended while parts of four other lines — including the Piccadilly Line serving Heathrow Airport — were closed.

Commuters shaken by the attacks regarded their neighbours with suspicion as they rode the Underground on Monday.

&#34I was a bit hesitant at first, but I have to use the Tube to get to work,&#34 said 20-year-old office worker Daniel Jakes. &#34People were glaring at each other, so I did feel a bit paranoid.&#34

Muslims in Britain fear a backlash from the bombings as Archbishop of Canterbury Rowan Williams, spiritual leader of the Church of England, warned they must not be made &#34scapegoats.&#34

The Muslim community and the police have reported several attacks on mosques since Thursday”s deadly bombings, which the authorities suspect were carried out by Islamic militants linked to Osama bin Laden”s Al-Qaeda network.

Blair said he was proud of the contribution to British society made by Muslims and promised to work with them to promote the &#34moderate and true voice of Islam.&#34