Egyptian riot police fired tear gas and live ammunition overnight to disperse thousands of pro-Palestinian protesters outside the Israeli Embassy in Cairo, and a security official said today that at least 20 demonstrators were arrested.

The rally in Cairo followed calls on Facebook for Arabs to march on Israel yesterday in support of the Palestinians, who were holding annual ceremonies marking the "nakba," or "catastrophe" — the term Palestinians use to describe their defeat and displacement in the war that followed Israel's 1948 founding.

Egypt's Health Ministry said at least 353 people were hurt outside the embassy, mostly from smoke inhalation. A security official said that some protesters sustained bullet wounds and that one protester was in critical condition. The official spoke on condition of anonymity because he wasn't authorized to talk to the media.

The protesters set fire to an Israeli flag, chanted anti-Israeli slogans and called for the expulsion of Israel's ambassador and the closure of the embassy.

A youth organization, which played a key role in the uprising that toppled former Egyptian President Hosni Mubarak, said on its Facebook page that the protest in front of the embassy was "civilized," and questioned the riot police's use of force in dealing with the demonstrators.

A witness, who wouldn't give his name fearing reprisals, claimed the police used unjustified force.

Egypt's state-run news agency MENA said the protesters managed to push aside barricades placed around the embassy building and attempted to storm the embassy itself to tear down the Israeli flag, which prompted the police action.

Security forces had used trucks and barricades to close off at least three main roads leading to the embassy, located in the Cairo suburb of Giza.