Tens of thousands of people have gathered in London and other European cities to mark the second anniversary of the war in Iraq with marches protesting the U.S.-led invasion.

Police estimate that up to 45,000 people took part in the largest march, held in central London. It began at Hyde park, passed the U.S. embassy and ended with a rally and anti-war speeches in Trafalgar Square.

Prime Minister Tony Blair has been a key ally of President Bush in the war in Iraq, a stance that is threatening his political future as Britain prepares for a general election expected in May.

Anti-war demonstrations are also being held in other European cities. In Turkey, several hundred people rallied in Istanbul, Adana and Ankara to demand that U.S. troops leave Iraq. In Sweden, several hundred people chanted, "U.S.A. out of Iraq" at a demonstration in Stockholm.