( CNN ) -- Thousands of demonstrators marched through cities across Europe on Saturday , calling for an immediate end to Israel 's attacks on Gaza . A protester swings a club at a police horse Saturday night near London 's Israeli Embassy . Up to 20,000 people were gathered outside the Israeli Embassy in London , England , at the peak of protests there , London Metropolitan Police said . A police officer was knocked unconscious Saturday night as the protests turned unruly , the police said . The London crowd dismantled barriers placed in front of the embassy and began pelting officers with sticks , rocks and pieces of the metal barriers , police said . Three people were arrested . Organizers including the Stop the War Coalition and the Palestine Solidarity Campaign expected more than 100,000 people to join the London march to protest Israel 's ongoing attacks on Gaza . Celebrities including musician Annie Lennox and Bianca Jagger , musician Mick Jagger 's ex-wife , spoke at a rally before the procession , which went from Hyde Park to the Israeli Embassy in Kensington , West London . Watch demonstrators throw bottles , metal at police » . Lauren Booth , the sister-in-law of former Prime Minister Tony Blair , also spoke at the rally , The Times newspaper reported . During her speech , Booth criticized Blair over his attempts to bring about a resolution to the conflict . `` Tony Blair 's only comment regarding the cease-fire has been to say that it can only take place after the tunnels in Gaza are destroyed , '' The Times quoted her as saying . `` What he is suggesting means that after the massacre , people will have no access to food , kerosene and medicines that came through those tunnels . That is not a cease-fire ; that is a slow agonizing death , '' she said , according to The Times . Former London Mayor Ken Livingstone issued a statement backing the demonstration . `` Every day , we see appalling pictures of children slaughtered by Israeli bombs , missiles and other sophisticated weapons , '' he said . `` Yet with more than 700 dead and thousands more seriously wounded , the international community is allowing Israel to continue its completely disproportionate onslaught accompanied by an Orwellian litany of lies . '' Meanwhile , the British Press Association reported that similar demonstrations took place in other British cities , including Newcastle and Edinburgh . Thousands took part in a rally through the center of Edinburgh calling for an end to the military campaign . About 300 shoes and red paint were thrown toward the U.S. consulate in the Scottish capital , the PA said . Thousands demonstrated in other European cities , according to local media reports , including Innsbruck , Austria ; Paris , France ; Milan , Italy ; Berlin , Germany ; and Oslo , Norway . iReport : Protests in Paris . In Washington , pro-Palestinian activists rallied outside the temporary residence of President-elect Barack Obama on Saturday and called on the incoming leader to stop the violence in Gaza . About 3,000 people carrying signs and chanting `` Free Palestine '' flooded Lafayette Park between the White House and the Hay-Adams Hotel , where the president-elect is living with his family . Carrying a flag and wearing a Palestinian keffiyeh head scarf , Abdel-Kader Elkabil exhorted the president-elect to take action . `` Please , Mr. Obama , do something . We love you . We voted for you , '' he said . `` I 'm expecting you to do something . ... You 're the only one who can do something . '' Asma Mobin-Uddin drove to Washington with a group of 500 activists from Ohio . She said she voted for Obama because she believed he could `` make a difference . '' `` President Obama , look in the eyes of your kids and look in the eyes of the kids in that region , '' she said at the rally . `` Please , stop the violence , stop the hate , stop the occupation . '' Israelis say their Gaza military operation , which started December 27 , is targeting rocket-launching sites , Hamas infrastructure and the movement 's leaders in an effort to stop militants from sending rockets into southern Israel . Palestinian medical sources said that more than 800 Palestinians have been killed in the attacks , including 235 children , and about 3,300 people have been wounded . Thirteen Israelis , including 10 soldiers , have died since the operation began . CNN 's Rachel Streitfeld and Mona Larijani contributed to this report .
Three days after London protest becomes unruly ; officer call out . Police estimate 20,000 protest outside US Embassy in London . Similar protests take place in other European countries . 3,000 protest outside temporary residence of U.S. President - elect Obama .