(Reuters) -- Syrian and Libyan demonstrators hurled rocks, eggs and tomatoes at the Chinese embassy in Tripoli on Monday, after Russia and China vetoed a U.N. Security Council resolution backing an Arab plan urging Syria's President Bashar al-Assad to give up power.

Armed men, who said they were from the Libyan government's Supreme Security Committee, guarded the embassy from about 50 protesters who waved Syrian opposition flags and had managed to break windows and spray graffiti on the walls.

One demonstrator tried to force his way past the guards but was stopped, a Reuters reporter said.

Just as protesters had done the day before at the Russian Embassy, demonstrators said they wanted to take down the Chinese flag and replace it with the Syrian opposition's flag and the red, black and green flag of Libya's National Transitional Council, which came to power after a civil war last year that toppled and killed Moammar Gadhafi.

All of this is because of what is happening in Homs, this is because of the Chinese and Russian veto, said Ahmed Mourad, a Syrian expatriate in Libya.

One of the men guarding the embassy said his colleagues had shot into the air to disperse the crowd when they hurled rocks and tried to push their way through. The crowd later hurled eggs before lining up to pray at prayer hour.

A Reuters reporter was let inside the compound. A Chinese security guard who spoke to him at the door of the embassy building and gave his name as Ibrahim said: We are fine.

A Libyan government guard parked a vehicle mounted with an anti-aircraft gun in front of the door of the compound, pointing outwards, and placed the Syrian opposition and Libyan NTC flags in the barrel to loud cheers from the crowd.

The demonstrators later handed a hand-written letter to the Libyan guards to give to Chinese officials inside, in which they said they criticized China's veto. The crowd later dispersed.

On Sunday, Libyan and Syrian demonstrators sprayed graffiti on the walls of the Russian Embassy in Tripoli and tore down its flag. Men replaced the Russian flag with that of the Syrian opposition and the NTC.

China defended its rejection of the U.N. draft resolution, with state media saying Western armed intervention in Libya, Afghanistan and Iraq exposed the risks of forced regime change.

Syrian forces bombarded Homs on Monday, killing 50 people in a sustained assault on several districts of the city which has become a centre of armed opposition to Assad, the Syrian National Council opposition group said.