Scores of opponents of Syrian President Bashar al-Assad's regime stormed the Syrian embassy in Cairo on Friday before being dragged away by security forces, an AFP reporter said.
At least 200 protesters forced their way into the building in the Garden City neighbourhood in Cairo, breaking doors and windows, before Egyptian security officials arrived and took them out. No arrests were made.
The embassy was empty because Friday is a weekend day in Egypt.
Syrian Ambassador Yusef Ahmed headed to embassy after the incident and said he would formally complain to the authorities.
"The Syrian embassy is being targeted. We will be sending a formal letter calling for the embassy to be protected. The protection today was very weak," Ahmed told AFP.
The protesters "went into the building. They reached the floor where the ambassador's office is located. Unfortunately they were not resisted," he said as he walked over broken glass and into the building.
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"This is a very serious development," he said.
Ahmed said protesters had already stormed the ambassador's residence in recent weeks, when it was also empty.
"It is the same people. We have given a list of names to the authorities, but no measures have been taken," Ahmed said.
The storming of the embassy and the lack of protection point to a "development that does not suit the brotherly relations between Egypt and Syria," Ahmed said.
Syria has been gripped by violence since March, with a regime crackdown on dissent leaving more than 5,400 dead including 384 children, according to UN figures.
The head of the Arab League monitoring mission in Syria said that, since Tuesday, unrest had soared "in a significant way," especially in the flashpoint central cities of Homs and Hama and in the northern Idlib region.
The latest wave in the government crackdown, now in its 11th month, comes as the West tries to ride diplomatic momentum sparked by last weekend's surprise call by the Arab League for Assad to step down.
Western and Arab nations were to hold talks in New York later Friday on a draft resolution denouncing the Assad regime that has been blocked by strong resistance from Damascus allies Beijing and Moscow.