LONDON (AFP) - World leaders wrangled Wednesday about how to fix the global economy, as anti-capitalist protesters attacked a bank in central London on the eve of a crunch G20 summit. Demonstrators laid siege to the Bank of England and smashed the windows of a nearby bank that has become a symbol of the financial crisis in Britain, which has been hit hard by the credit crunch and its economic fallout. Security is water-tight ahead of Thursdays (today) Group of 20 summit, where leaders including US President Barack Obama are struggling to overcome US-Europe tensions over how to ease the global slowdown. Several thousand demonstrators invaded Londons main financial district and tensions spilled over when protesters smashed their way into an office of Royal Bank of Scotland, which was taken into state ownership last year. Scum and Beat inflation - eat the rich, were sprayed in graffiti on the outside of the branch, which was closed for the day. Police said they made 19 arrests in the clashes, which came as world leaders held pre-summit talks trying to iron out differences over whether tighter regulation or further fiscal stimulus would do more to ease the crisis. At one point a protestor in a black balaclava pulled himself up to get into a window of the bank, but a policeman wielding a riot shield repelled him from inside. Outside the Bank of England, activists scuffled with police, hurling taunts, paint bombs and fruit, while police responded with occasional baton blows to keep the masked demonstrators back. The Times newspaper described the pre-summit security lockdown as Fortress London while the City AM newspaper ran the front-page headline: G20: A City Under Siege. France and Germany demanded tough action by the summit and Obama warned the United States could no longer be counted on to be the voracious consumer which would lead worldwide growth. French President Nicolas Sarkozy said France and Germany rejected the current summit proposals on reforming the financial system and cracking down on tax havens and corporate bonuses. But other leaders played down his threat to walk out of the summit which even the German government said was not the best idea. Im confident that President Sarkozy will be at the first course of the dinner and that he will complete the dinner, said British Prime Minister Gordon Brown of the threat, referring to a pre-summit leaders meal at Downing Street Wednesday night. Sarkozy and Brown held telephone talks Wednesday ahead of the summit and agreed on the need for tougher world finance rules, the French presidency said. But Sarkozy said before leaving Paris there had been no agreement on a summit communique. Neither France nor Germany are satisfied with the proposals as they currently stand, said the French leader. I will not associate myself with a false summit, that concludes with a statement of hollow compromises, that does not address the problems that we face. Obama and Brown, who is struggling to bridge the summit gap between the US and Europe, played down the differences but not the scope of the crisis that the summit will have to confront. Make no mistake, we are facing the most severe economic crisis since World War II, and the global economy is now so fundamentally interlinked that we can only meet this challenge together, said the US President, who has also held his first face-to-face meetings with Russias President Dmitry Medvedev and Chinas President Hu Jintao. German Chancellor Angela Merkel voiced her concern before leaving Berlin. I am going to London with a mixture of confidence and concern. Concern on one hand on whether we can really react to the serious situation... Confident, however, that... we cannot stick our heads in the sand, she said. Merkel has spoken out against governments like the US and Britain spending their way out of the crisis. But her fears were dismissed by Prime Minister Taro Aso of Japan, whose country spent massively spent to re-ignite the economy following the Asian financial crisis. Because of the experience of the past 15 years, we know what is necessary, while countries like the US and European countries may be facing this sort of situation for the first time, he told the Financial Times.