In London, thousands of placard-waving activists rallied to demand a halt to the conflict between Israel and Hezbollah in Lebanon.
The demonstration passed the US embassy and Downing Street as Tony Blair, the British prime minister, worked inside on securing a United Nations resolution aimed at ending the bloody conflict.
London's Metropolitan Police said 20,000 people were on the protest, while the organisers, the left-wing Stop the War Coalition, claimed a turn-out around 100,000-strong.
Stop the War spokesman John Rees told AFP that the protest was to hammer home a message to Blair.
"It's about telling the British and US governments that we want an unconditional cease-fire. We're the people who have the power to stop the Israelis in Lebanon," he said.
"Their silence is permitting mass murder in Lebanon by the Israeli forces. Look at the casualties: it's eight to one."
More than 1,000 people also demonstrated across the French cities of Paris, Lille in the north and Strasbourg in the east calling for an end to "the massacre of the Lebanese people".
Some 400 people gathered in central Paris carrying banners reading "stop the massacres" and "a cease-fire in Lebanon" walking behind Lebanese and Israeli flags.
Another 500 demonstrated in Strasbourg, with young demonstrators marching behind two coffins adorned with pictures of children injured in the Israeli onslaught of Lebanon.
In the northern city of Lille, some 400 demonstrated according to police and some 800 according to organisers, to denounce "the international community's silence" over the "massacre".
"It's about telling the British and US governments that we want an unconditional cease-fire. We're the people who have the power to stop the Israelis in Lebanon"
Stop The War spokesman
Two Jordanian policemen and two protesters were slightly injured in clashes in the capital Amman during an anti-Israeli protest, police spokesman Major Bashir al-Daajeh said in statements published on Saturday.
The police also briefly detained eight demonstrators before releasing them on bail on charges of attacking law enforcement agents during Friday's "unauthorised" demonstration, Daajeh told Al-Ghad newspaper.
He said the clashes broke out when around 200 people gathered outside a mosque in west Amman in an attempt to march on the nearby Israeli embassy to denounce the ongoing Israeli onslaught on Lebanon.
"The police asked them to leave and when they refused they used clubs to break up the demonstration," Daajeh said.