The Cairo crowd smashed furniture and equipment and set fire to parts of the embassy building overnight.
In London, about 150 protesters chanting “the embassy we want” tried to force their way into the Syrian compound as police in riot gear battled to hold them back.
They tore down the flag outside and hurled missiles, smashing windows of the building in an echo of a similar demonstration ovenight when five men were arrested after successfully breaking into the building while another was held for assaulting police.
British authorities condemned the protests and said police were reviewing security arrangements.
Syrian residents in Kuwait broke into the embassy there at dawn on Saturday, ripping down the flag and injuring several security guards, the state news agency KUNA reported.
Rallies also broke out outside Syrian embassies in Germany, the United States, Greece and Libya after human rights activists reported that more than 200 people were killed in a shelling of the city of Homs by government forces.
The gate of the embassy in central Cairo was broken and furniture and computers were smashed on the second floor of the building. Parts of the first floor were burned.
The scene was calm by early Saturday morning and Egyptian police were guarding the embassy. Embassy official Ammar Mohamed said he had been told by security officials about the overnight attack and arrived at the site to assess the damage.
Hundreds of demonstrators gathered at a police station a few streets away to demand the release of as many as 11 Syrians and an Egyptian who they said were detained during the protest at the mission.
“God you are so strong, help us secure victory over Bashar!” chanted protesters outside the Cairo police station where they said the detainees from the demonstration were taken.
In Berlin, some two dozen people rushed past a police barricade and broke into the Syrian embassy, smashing portraits of Assad and his father and hanging a flag of the Free Syrian Army from a window.
Minor scuffles broke out at the Russian embassy in the French capital on Saturday during a pro-Assad demonstration.
About 20 supporters of the Syrian president were confronted by about 50 people against the government, according to a Reuters witness. Nobody was injured, but the police stepped in to make some arrests. An anti-Assad demonstration was also due to take place later on Saturday in central Paris.
A live Internet stream from the Washington rally showed dozens of people shouting “Syria soon will be free.”
In Athens, 12 Syrians and one Iraqi were detained for throwing stones at a guard post outside the Syrian embassy, a Greek police official said. They were expected to be released later in the day.
In Tripoli, some 50 protesters, the majority of them Syrians, climbed over the walls of the Syrian embassy compound and opened its outer gate. A small group climbed on top of the building to pull down the Syrian national flag and replace it with that of the Syrian opposition.
There were no employees at the embassy on Saturday, where only consulate staff now worked, a security guard said. Libya’s National Transitional Council said in October it officially recognized the Syrian opposition council as the legitimate authority in Syria after months of unrest against Assad.
Anis Al-Khaled Al-Asmar, a member of the Syrian opposition group based abroad, the Syrian National Council (SNC), said the demonstrators planned to take over the embassy.
Essam Suleiman, a Syrian from Damascus who has lived in Libya for 20 years, said: “The Libyan government said they recognize the Syrian opposition but the Syrian embassy is still flying the flag and they are still working inside the building.”
Syrians have held regular protests outside the Cairo headquarters of the Arab League, which has suspended Syria’s membership, imposed sanctions and sent Arab monitors to Syria to assess whether the government was heeding an Arab peace plan.
The League called on Assad to step aside and hand powers to a deputy to start a dialogue with the opposition. Arab officials traveled to New York to seek UN Security Council backing for the resolution.
