Barack Obama has hailed the G20 summit as a historic turning point in the pursuit of world economic recovery.

Leaders pledged new spending and tougher financial regulations, in what the US leader called an unprecedented set of actions to ease the crisis.

He now heads to Strasbourg for talks with the French and German leaders, before a Nato summit begins.

Security is extremely tight in the city, with tens of thousands of troops and police deployed.

On Thursday police clashed with protesters, firing tear gas and rubber bullets to stop a crowd getting to the city centre.

Masked protesters smashed bus shelters and set fire to rubbish bins. French news agency AFP reported around 100 arrests.

Nato talks

Speaking at a news conference in London late on Thursday, Mr Obama said that the G20 leaders had agreed "unprecedented steps to restore growth and prevent a crisis like this from happening again".

NEW FUNDING PLEDGES
$500bn for the IMF to lend to struggling economies
$250bn to boost world trade
$250bn for a new IMF "overdraft facility" countries can draw on
$100bn that international development banks can lend to poorest countries
IMF will raise $6bn from selling gold reserves to increase lending for the poorest countries
Source: BBC

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They pledged a total of $1.1 trillion (£681bn) in funding to tackle the crisis, including $750bn to the International Monetary Fund, $250bn to boost global trade and $100bn for international development banks to lend to the poorest countries.

Leaders also agreed to introduce tougher financial regulations and sanctions against secretive tax havens.

"This was the day the world came together to fight back against global recession," said Gordon Brown, the host of the summit.

Representatives from the developing world welcomed the outcome.

Brazilian President Luiz Inacio Lula da Silva told the BBC's Newsnight programme that rich countries had engaged with emerging nations on "equal terms" to achieve a good result.

French President Nicolas Sarkozy - who had threatened to walk out of the meeting if it did not yield concrete gains - said that the conclusions were "more than we could have hoped for".

He will meet Mr Obama for one-to-one talks on Friday, after which the US leader will cross into Germany for a meeting with Chancellor Angela Merkel.

Then the focus will turn to Nato and the 60th anniversary summit that is being hosted jointly by France and Germany.

Leaders will gather for a working dinner in the German city of Baden Baden on Friday night before the main talks on Saturday.

The US president is expected to use the opportunity to build support for his new strategy for Afghanistan.

More troops are needed certainly, says the BBC's diplomatic correspondent Jonathan Marcus, but above all the Americans want to see their allies stumping up a good deal more money and more training teams to build Afghanistan's own security forces.