Demonstrators hurled shoes at the tall iron gates outside the British prime minister's residence in London on Saturday and waved Palestinian flags in more than a dozen European cities as tens of thousands protested Israel's operation against Gaza terrorists. In London, at least 10,000 people, many carrying Palestinian flags, marched past Prime Minister Gordon Brown's Downing Street residence to a rally in Trafalgar Square. Outside Downing Street, hundreds of protesters stopped and threw shoes at the gates that block entry to the narrow road. Shoe-throwing has become a popular gesture of protest and contempt since an Iraqi journalist pelted US President George W. Bush with a pair of brogues in Baghdad last month. Police estimated the crowd in London at 10,000 to 12,000, but organizers said the number was much higher. The marchers included activist Bianca Jagger, ex-Eurythmics singer Annie Lennox and comedian Alexei Sayle. "As a Jew, it's very moving to see so many people who are so outraged at Israel's actions," Sayle said. "Israel is a democratic country that is behaving like a terrorist organization." After the rally, a smaller group of about 2,000 protesters marched on the Israeli Embassy in west London, and some youths scuffled with police and hurled objects at officers in riot gear. Police said there were no initial reports of arrests. Rallies also were held in other British cities - including Manchester, Liverpool and Glasgow - and across Europe in countries such as Italy, Germany and Turkey. Turkish Prime Minister Recep Tayyip Erdogan flew to Saudi Arabia as his country engaged in shuttle diplomacy with Arab countries to help broker a cease-fire. But public anger mounted in Turkey, as 5,000 Turks shouting "Killer Israel!" protested in downtown Ankara. In The Netherlands, thousands of people marched through Amsterdam, criticizing both the Israeli attacks and the Dutch government's failure to condemn them. One banner declared: "Anne Frank is turning in her grave. Oh Israel!" More than 4,000 people demonstrated in Duesseldorf, Germany, and some 5,000 in Frankfurt. One group in Duesseldorf held up a doll representing a bleeding baby with the placard "Made in Israel." In Berlin, more than 7,000 people braved freezing temperatures for a march along the capital's Unter den Linden boulevard. Another 2,500 demonstrated in Salzburg, Austria, while scores protested peacefully in Madrid outside the Spanish Foreign Ministry. Hundreds more marched in the Swedish cities of Malmo and Uppsala, while in Oslo, Norway demonstrators marched from the parliament to the Israeli Embassy, calling on Israel to "let Gaza live." Most of the protests were peaceful, but in Athens, Greece - the scene of violent demonstrations by anarchist youths over the past month - a few of the 5,000 protesters threw stones and petrol bombs at police outside the Israeli embassy. Riot police retaliated with tear gas and stun grenades. In Cyprus, demonstrators pelted riot police with rocks, sticks, shoes and oranges near the Israeli embassy in Nicosia. A peaceful protest by about 2,000 people turned violent when some protesters tried to break through a line of police blocking the road leading to the embassy. The demonstrators eventually dispersed. Brown's office said Saturday the British leader had phoned Prime Minister Ehud Olmert and called for an immediate cease-fire. "Rocket attacks from Hamas must stop, and we have called for a halt to Israeli military action in Gaza," a spokesman said on condition of anonymity in line with government policy. "Too many have died and we need space to get humanitarian supplies to those who need them."