Iranian security forces on Monday fired tear gas to disperse protesters who gathered at a Tehran square in support of demonstrations in Egypt and Tunisia, which was later turned into an anti-government demonstration, a witnesses said.

Sporadic clashes were also reported to have taken place on Enghelab Square in central Tehran, between security forces and opposition protesters. The demonstration on Monday was called by the opposition leaders Mir-Hussein Mousavi and Mehdi Karroubi, in support of Egypt an Tunisia's uprising.

People in separate groups, silently and without chanting slogans, were moving towards Tehran's Azadi (Liberty) square but the security police forces chased to disperse them, according to witnesses.

Another demonstration were also reported by witnesses, around Imam Khomeini Square.

Security measures were high on Tehran's Haft-e-Tir Square and on Karim Khan and Vali-e-Asr streets, said Xinhua reporters.

Iran's opposition leaders asked for an official permission to demonstrate on Monday to back popular protests in Egypt and Tunisia, which was rejected by the government.

However, the opposition leaders insisted on their demand defying the government's rejection.