Tony Blair and George Bush have spoken of their joint determination to defeat terrorism after bomb attacks in Turkey.
The leaders condemned the 'evil' of the Turkey terror attacks
The UK prime minister said the blasts showed "the evil these terrorists pose to innocent people everywhere".
The perpetrators had "utter contempt" for innocent lives, said the US president at a news conference held to mark his state visit to Britain.
Both men vowed to stay the course in Iraq, with Mr Blair saying they would not "flinch or concede one inch".
"We stand absolutely firm until this job is done, done in Iraq, done elsewhere in the
world," the prime minister added.
Contrary to some predictions, the two leaders announced no definite moves on either the British detainees in Guantanamo Bay or the dispute between the European Union and US over America's imposition of tariffs on steel imports.
The joint news conference, at the Foreign Office in London, came shortly before thousands of demonstrators took to nearby streets for a march and rally to protest at Mr Bush's visit.
But his appearance alongside Mr Blair in front of reporters was dominated by the bomb attacks in Istanbul.
The British consulate and the headquarters of the London-based HSBC bank were targeted, leaving more than 20 dead - including the British consul-general - and hundreds injured.
Speaking first, Mr Blair said the attacks demonstrated "the evil these terrorists
pose to innocent people everywhere".
"Once again we must affirm that in the face of this terrorism there must be no holding back, no compromise, no hesitation in confronting this menace, in attacking it wherever and whenever we can and in defeating it utterly."
President Bush declared: "The nature of the terrorists is evidenced
once again - we see their utter contempt for innocent life. They hate freedom,
they hate free nations."
He said the terrorists' cruelty was part of their strategy as they hoped "to intimidate, they hope to demoralise free nations... they're not going to succeed".
Also in the news conference:
- Mr Blair rejected any suggestion the UK and United States brought such attacks on themselves, saying "America did not attack al-Qaeda on September 11, al-Qaeda attacked America".
- Mr Blair vowed to "stand side by side with the United States of America to rid our
world of this evil once and for all".
- President Bush vowed to "finish the job we have begun" in Iraq, and said he still hoped to hand over power to a new Iraqi Government next year.
- The president said the number of US troops in Iraq would depend on what commanders on the ground considered necessary to secure the country.
- Asked why so many people in Britain appeared to fear or even hate him, the president said: "I fully understand people don't agree with war. But I hope that they agree with peace, and freedom, and liberty."
- On the Britons detained at Guantanamo Bay, Mr Blair said discussions were still going on over whether they would be tried by US military tribunals or brought back to the UK.
- The president referred to them as "illegals picked up off of the battlefield" but said they were "working with the British Government" on the issue.
- Mr Bush said the prime minister had raised the dispute between the European Union and US over steel tariffs "not once, not twice, but three times".
- He said: "I am reviewing the findings about the restructuring of our steel
industry... and will make a timely decision."
Mr Bush also paid tribute to British servicemen who died in Iraq.
Earlier, on a visit to Westminster Abbey, Mr Bush held a private meeting with some of their relatives, and also laid a wreath at the Tomb of the Unknown Warrior.
Aids task force
His motorcade then took the short journey to Downing Street, where Mr Bush and his wife Laura were warmly greeted by the prime minister and his wife, Cherie, before the leaders held around an hour of talks followed by the news conference.
Lunch in Downing Street was cooked by TV chef Nigella Lawson, with roast pumpkin, braised ham and apple pie on the menu.
Afterwards the two men held talks with representatives from several African countries and announced the launch of a joint task force on HIV/ Aids aimed at ensuring funding is well spent in the worst affected places.
As he left Downing Street at around 1530 GMT, Mr Bush was asked by reporters if he was enjoying his trip. Smiling broadly he replied: "Absolutely."
Later he is due to host a banquet for the Queen at the home of the US ambassador to Britain.