The death toll of British tourists caught up in the explosion which has killed 188 people in Bali is expected to rise to 33.

Foreign secretary Jack Straw said on Monday he was "as certain as he can be" that 18 British people have been killed in the Bali explosion, 15 are missing - believed to be dead and 27 are injured.

Prime Minister Tony Blair said the incident showed that the world was still under threat from terrorism.

We saw this huge explosion and a great big mushroom of flames go up

Nikki Bloomfield, British survivor

Meanwhile, British tourists returning from Bali have been describing their terrifying ordeal following the nightclub bombing.

Three-quarters of the victims killed in the attack on a beach resort nightclub are thought to be Australians.

The Foreign Office said four Britons who were unaccounted for have since turned up safe and well in Bali.

Officials named one of the dead as Marc Gajardo, 30, from Cornwall. His relatives, who live in the Truro area, have been informed.

Nikki Bloomfield, 27, from Sunninghill, Berkshire, who returned to the UK from Bali on Monday, said she witnessed the carnage.

She said: "There were just people lying around with bandages round their heads and their legs, covered in blood."

Seven Britons in a touring amateur rugby team from Hong Kong are feared dead.

The six men and one woman were last seen in the nightclub, a spokeswoman for the Hong Kong Rugby Football Union said.

Marc Gajardo died in the explosion

The Foreign Office is urging people to avoid travelling to Indonesia.

The device exploded late on Saturday night outside a crowded nightclub in the resort of Kuta which is popular with foreign tourists.

No-one has claimed responsibility for the attacks, but the US embassy in Jakarta recently issued warnings of possible attacks by Islamic militants linked to al-Qaeda.

Condemning the attack, Tony Blair said: "Terrorism has once again scarred the world.

"Saturday's outrage shows the kind of threat the world faces from terrorism - extremism knows no boundaries, shows no respect for human life or democratic values.

"We have played a full role in the fight against terrorism since 11 September and will continue to do so to protect the civilised values we hold dear."

Forensic teams

Jack Straw was equally robust in his denunciation.

He said: "This is a desperate and terrible act of terrorism aimed at entirely innocent people who have no argument with these terrorists and even if they were to, it's no way to conduct a political dispute.

"I utterly condemn this terrorism and the dreadful loss of life and the injuries."

Helpline numbers

British Consulate: 00 62 361270572 Foreign Office: 0207 0080000

A team of British forensic and counter-terrorism specialists are on their way to Kuta to help with the investigation.

The Metropolitan Police said a team of officers from its anti-terrorist branch were also travelling to Singapore.

Detectives are appealing for information from anyone who has returned from Bali in the last few days.

The Muslim Council of Britain has strongly condemned the bombing and urged the authorities to punish those responsible.

Nikki Bloomfield saw the blast from her hotel

UK tour operators are preparing to fly home some of the 1,000 British tourists who were on Bali, while holiday companies are arranging alternative destinations for holidaymakers booked to visit Indonesia in the coming days.

Keith Betton, from the Association of British Travel Agents, said he thought the explosion would not deter holidaymakers from visiting the region.

He said: "It could be a couple of years before the island recovers. But it will recover.

"I don't think people are going to be put off visiting Muslim countries.

The British Consulate in Bali has set up a 24 hour telephone number for people anxious about relatives or friends in Kuta.

The 24 hour telephone number set up by the British Consulate in Bali for people anxious about relatives or friends in Kuta is 00 62 361 270 572.