French president Nicolas Sarkozy embraced the White House hopeful as a "friend" when the Barack Obama express arrived in France.

The US Democratic candidate for presidency, who later flew on to London where he will hold talks with Gordon Brown today, pressed forward on an international tour aimed at reassuring American voters he is best equipped to make the US secure, and help mend rifts with key allies - including France - frustrated with eight years of unpopular Republican policies.

At a joint press conference with the French President in Paris, Mr Obama said Iran should not delay in resolving its dispute with the West.

The Illinois senator said Tehran should promptly accept an international call to freeze its "illicit nuclear programme". It should not wait for the election of a new US president before accepting the proposals made by Mr Sarkozy and other Western leaders "because the pressure is only going to build".

The US and other Western nations accuse Iran of seeking to acquire nuclear weapons, and demand that it freeze its uranium enrichment programme. Iran says its nuclear campaign is peaceful.

Mr Obama said that he and President Sarkozy agreed that Iran poses "an extraordinarily grave situation".

He added: "My expectation is we're going to present a clear choice to Iran: change your behaviour and you will be fully integrated into the international community.

"Continue your illicit nuclear programme and the international community will ratchet up pressure with stronger and increased sanctions."

Mr Sarkozy said there was a "tremendous convergence" of views in his meeting with Mr Obama. The White House hopeful had told reporters that "Afghanistan is a war we have to win" and the French President said he agreed that the Taliban must be defeated.While the French leader boasts a good relationship with Mr Obama - he called his guest "my dear Barack Obama" and has been quoted as calling him "my buddy" - Mr Sarkozy refrained from endorsing him in the presidential race. He wished the US candidate luck but said it was up to Americans to choose their president.

Asked how he would differ from US president George W Bush on foreign policy, Mr Obama pointed out that he is a senator, not president.

"What I can say is that an effective US foreign policy will be based on our ability not only to project power, but also to listen and to build consensus," he said.

Mr Obama then boarded a plane to London where he spent the night at the five-star Hyatt Regency London - The Churchill.

Just after 10pm the White House hopeful arrived at the £300 to £500-a-night hotel near Marble Arch in a convoy of four black Mercedes people carriers.

Six security staff blocked the entrance to the hotel as Mr Obama stepped out of the car and into the hotel lobby, unseen by the handful of tourists waiting outside to take pictures.

Today the Obama tour will conclude with talks with Mr Brown, Conservative leader David Cameron and Tony Blair, now Middle East envoy.

Seeking to burnish his foreign policy credentials for the campaign against Republican rival Senator John McCain, Mr Obama's trip began with a tour of the war zones in Iraq and Afghanistan.

He then visited Israel before delivering a public address in Germany on Thursday. Mr McCain has often sought to capitalise on his rival's lack of foreign policy experience.