The Obama/Medvedev statement in full | European demands threaten to wreck deal | COMMENT: Two and a half cheers for a G20 triumph | ANALYSIS: summit brinkmanship rings hollow | Day of mayhem | Obama's whirlwind of diplomacy | GRAPHIC: what they really meant | Welcome to the city, spruced and sanitised | G20: live blog

Russia and America have pledged to slash their nuclear stockpiles in a groundbreaking agreement in London on the eve of the G20 summit.

President Obama and President Medvedev issued a statement that promised a “fresh start” in relations that could include a legally binding arms reduction treaty by the end of the year. White House officials indicated that the number of nuclear warheads was likely to be reduced to no more than 1,500 each.

It was the first time that the two leaders had met. Mr Obama will visit Moscow in the summer.

The four-page statement pledged co-operation on issues ranging from the war in Afghanistan to reining in Iran’s nuclear ambitions. However, White House officials said that the men disagreed on human rights, US plans to site missile defence systems in Eastern Europe, the expansion of Nato and Russia’s invasion of the Georgian territory of South Ossetia.

Mr Obama set a hectic pace in his debut to the world stage. He held his first talks with the Chinese President Hu Jintao. China, which has been pushing for more say in the governance of global institutions at the expense of Europe, has already signalled that it may be willing to pour billions of dollars into the IMF to help developing economies.

Meanwhile, Gordon Brown’s hopes of securing a comprehensive economic recovery plan hit a dangerous hitch. President Sarkozy of France and Angela Merkel, the German Chancellor, joined forces at a London hotel to warn that they would not sign up unless their call for a new international “financial architecture” was met. In what may yet turn out to be an exercise in pre-summit brinkmanship, they said that agreement had to come today and could not be put off to a later summit.

The day was marred by protests in the City of London. Although fears of a mass riot failed to materialise, masked anarchists smashed their way into a branch of Royal Bank of Scotland. By 7pm, 32 people had been arrested, 11 for possession of police uniforms while travelling in an armoured personnel carrier. A man, believed to be in his 30s, collapsed and later died near a police cordon. Bottles were thrown at officers who went to his aid.

In a joint press conference at the Foreign Office, Mr Obama praised Mr Brown’s leadership in bringing the summit to London. American officials voiced astonishment that, in the middle of intense negotiations, Mr Brown had to go to the Commons to face Prime Minister’s Questions. “We are constantly fascinated by the rituals and rigours of parliamentary democracy,” said one.

Times Recommends

• Fern Britton: 'I still can't see that I was wrong'
• Extreme cooking
• Easy French: Tarte Tatin