Similar protests have occurred almost daily in the Middle East and elsewhere since Israel launched its operation more than two weeks ago to stop rocket fire from the militant Palestinian group Hamas.
The demonstrations have been fueled by the rising death toll in Gaza, which currently stands at over 800 Palestinians. Thirteen Israelis have also died in the fighting.
Saturday's protests were largely peaceful, but three policemen were injured in London when some demonstrators began hurling missiles near the Israeli Embassy.
More than 60 people were injured during a large demonstration Friday in Algeria's capital, many by stone throwing, the Interior Ministry said.
In Norway, police used tear gas to try to disperse at least 1,000 protesters after some hurled bottles, rocks and fired fireworks at officers. Two people were injured and two were taken into custody, said Oslo police spokeswoman Unni Groendal.
Protesters in Sweden tried to break through sealed-off areas at Israel's embassy in Stockholm after a march through the city by 3,000 to 5,000 people. Some burned Israeli flags.
In Greece, more than 2,000 mostly Arab demonstrators, joined by several Greek leftist groups, marched to the Israeli embassy in protest.
In Innsbruck, Austria, volunteer security personnel arranged by the Islamic organizers of a demonstration moved quickly to surround and protect an elderly man after he suddenly unrolled an Israeli flag in the middle of the protest.
Thousands of demonstrators in the Scottish capital of Edinburgh gathered in front of the American consulate to toss shoes at the 19th century town house.
Sky News television footage showed police recoiling as a storm of shoes flew over their heads.
"They were just flying, like hail through the sky," protest organizer Ian Hood said in a telephone interview. He said protesters were angry at the U.S. for failing to stop the bloodshed in Gaza.
Ottawa was also criticized for failing to oppose the United Nations' call for an end to hostilities. A group of prominent Canadians, many of them Jewish, is calling on the government to demand an immediate cease-fire in Gaza.
The group said Israel's actions amount to war crimes, and that Canada
In London, police estimated 12,000 demonstrators rallied in Hyde Park in support of the Palestinian cause, carrying placards marked "Gaza: Stop the massacre" and chanting "Free, free Palestine." BBC News put the total at as many as 50,000.
Sky News reports that a policeman was knocked unconscious and two others injured as some protesters turned violent.
Protesters threw objects at police and smashed windows on Kensington High Street near the Israeli Embassy.
As riot officers charged at the group of mostly young men, sticks and barriers were hurled at the officers by the group, many of whom were masked.
Police cordoned off the area and siphoned off demonstrators, one by one, to have their picture and identification taken.
In France, thousands of protesters marched through Paris and other cities in favor of Gaza Palestinians, a week after 21,000 marched in the French capital for the same cause.
Demonstrators in Paris were crying out "We are all the children of Gaza" and brandishing Palestinian flags to protest Israel's deadly offensive.
There was no official estimate of the number present for the march from central to eastern Paris, but thousands were present.
Far-left politician Olivier Besancenot was among the marchers, as was the French Jewish Union for Peace.
Last week's march degenerated into violence in a main shopping district with cars burned and windows broken. Police changed the route this time around.
Demonstration Dubbed "Anti-Fascist"
Saturday's rally in the southern Lebanese town of Nabatiyeh was organized by the militant Hezbollah group, a strong ally of Hamas that fought its own war with Israel in the summer of 2006.
The thousands of demonstrators who marched through the streets waved Lebanese and Palestinian flags and some carried posters of bloody Palestinian children.
Meanwhile in Sarajevo, Bosnia, hundreds to the streets to call for an end to the Israeli military offensive in the Gaza strip.
"This demo is not anti-semitic, it is anti-fascist, because they are fascists what they are doing to people in Gaza," said Suada Abdoum. "We want peace for everyone, life and dignity for everyone including the poor Palestinians."
Sarajevo resident Emir Begic said, "I can't sleep since the bombing in Gaza started. I just keep my eyes closed, thinking about those people and their poor souls."
Hamas Leader: No Deal With Israel
Meanwhile, the rage within the Gaza Strip continued. A top Hamas leader said this evening that the Gaza war has killed the last chance for settlement and negotiations with Israel.
Damascus-based Hamas leader Khaled Mashaal gave a fiery speech on the Arabic news channel Al-Jazeera condemning Israel's attack on the Gaza Strip, describing it as a "holocaust."
Mashaal also called for an end to Israeli attacks, the removal of its forces from Gaza, and a lifting of the Gaza blockade.
In Gaza this morning,. The notice said Israel is about to begin a "new phase in the war on terror".
It said it will "escalate" an operation that already has killed more than 800 Palestinians.