As the search continues for the perpetrators of yesterday's attacks on London, police have put the death toll at 49, but expect it to rise.

It is understood that among the victims of the four attacks were nationals from China, Australia, Portugal, Poland and Sierra Leone.

Metropolitan Police Commissioner Ian Blair said that the death toll from the bomb blast on a London bus is 13, revising up a figure of two given yesterday.

The wreckage of the bus, with the roof torn off, is still on the street where it blew up. A large screen has been erected around the site.

Earlier, Mr Blair said there was great difficulty in determining a final death toll because of the damage at the blast scenes.

He added that there were 700 casualties, 350 people were taken to hospital, 22 are still in a critical condition and one person died in hospital.

Mr Blair said there was absolutely nothing to suggest that any of the attacks were carried out by a suicide bomber, although he added that nothing at this stage could be ruled out.

It has also been revealed that police have yet to reach one of the London underground train carriages where a bomb went off. 

The Assistant Police Commissioner, Andy Hayman, said there were safety concerns in the tunnel.

Police suspect al-Qaeda

Police investigating the attacks say early indications suggest they were carried out by al-Qaeda.

However, they have dismissed reports that the bombings were the work of a terror cell based in the Midlands as 'pure speculation'.

Claim taken seriously

Britain's Home Secretary Charles Clarke has said a claim of responsibility for the bombings is being taken seriously.

The claim was made by a previously unknown group calling itself the Secret Organisation of al-Qaeda's Jihad in Europe on its website.

It posted a message saying the blasts were in retaliation for Britain's involvement in Iraq and Afghanistan.

In a television interview, Mr Clarke said the claim was serious, although alternative explanations have not been ruled out.

A huge police investigation got underway today to find those responsible for the bombings. Police investigators are still working at the scenes of the attacks.

Three explosions occurred on underground trains, the fourth on the double-decker bus. It was the worst terrorist attack in Britain since the Lockerbie explosions 17 years ago.

Muslim leaders in talks

Muslim leaders in London were holding talks with police today amid fears of reprisals against their community. 

Most buses and a limited train service were operating in London this morning, but underground services remain curtailed. Transport for London has said many sections of the underground will not be fully restored for several weeks.

A large number of schools in London remained closed today.

Blair vows culprits will be caught

Yesterday, British Prime Minister Tony Blair pledged to bring those responsible to justice and said the way of life in Britain would not be affected.

While saying that the attacks appeared to have been carried out in the name of Islam, Mr Blair stressed that the vast majority of Muslims opposed terrorism.

The US Secretary of State, Condoleezza Rice, said those who carried out the attacks in London, and elsewhere, espoused an ideology of hatred.

She said there could be no peace deals with terrorists.

Fears that Denmark could be attacked

Denmark, one of the United States' staunchest allies in Iraq, is tightening security in the wake of the London blasts, amidst growing fears that it could be the next hit by a terrorist attack.  

'It is now not a question of whether or not Denmark will be hit by a terrorist attack, but when it is going to happen,' Copenhagen University security expert Mikkel Vedby-Rasmussen said.   

'I cannot look into a crystal ball and foretell the future of course but it seems unavoidable now and we must start preparing for the possibility,' he added.

NATO not asked for help

British authorities have not lodged a request for help from NATO after the attacks in London but the military alliance will be ready to aid if needed, Secretary General Jaap de Hoop Scheffer has said.

He said: 'The UK has not asked for invoking article five', referring to a clause in NATO's charter, which says that an attack on one member country is deemed an attack against all member countries.  

He added: 'The UK has indicated that they can cope, but whenever the UK might ask for assistance, NATO will be ready to give it'.

Five minutes of silence in Spain

The government and several cities in Spain observed five minutes of silence in memory of the victims of the attacks on the London transport system, which recalled Spain's worst terrorist attack just over a year ago.  

In a statement, the government said it wanted to demonstrate its solidarity with the victims and the British people and condemn yesterday’s attacks.  

The gesture, mirrored in several cities outside the capital Madrid, followed calls from the ruling Socialist Party and opposition conservative Popular Party.  

The attacks on the London Underground and a bus bore similarities to the 10 blasts on four packed early morning commuter trains last year in Madrid, which killed 191 people and injured 1,900.  

Both the Madrid and London attacks took place at rush hour, and the explosions took place almost simultaneously, indicating that they were carefully coordinated.

Security boosted in Thailand

Thai police have boosted security at subway stations, bus stops and shopping centres in the wake of the London bombings.  

Thailand had already boosted security at 256 potential targets for attack around the country after militants staged coordinated bombings of an airport, a hotel and a store in the southern city of Hat Yai on 3 April.

National police chief General Kowit Wattana said: 'As of now we do not detect any terrorist movement in Thailand. We can control the situation in Thailand and we are closely coordinating our intelligence with information from other countries.'