Iranian police fired in the air to disperse pro-reform demonstrators in central Tehran on Thursday, nearly four weeks after a disputed election triggered mass protests in the capital, a witness said.
The witness also said he saw police detaining several people among about 250 protesters who had gathered near Tehran University in defiance of a ban on gatherings for the anniversary of violent student demonstrations in 1999.
It appeared to be the worst outbreak of unrest in Tehran since security forces last month quelled days of opposition protests over the June 12 election, which moderate opponents of President Mahmoud Ahmadinejad say was rigged in his favour.
"Police are shooting in the air and they have arrested several people," the witness said.
Another witness at the scene in downtown Tehran said, "Police used tear gas twice to disperse the crowd. There were also many Basij militia on motorbikes patrolling the area."
Police urged passers-by through loudspeakers to leave the area, the witnesses said.
"They were about 250 people who shouted in favour of (defeated presidential candidate Mirhossein) Mousavi and made the victory sign. Police dispersed them," one witness said.
There was none of the chanting of slogans against the clerical elite that could be heard during protests in Tehran and other cities after last month's presidential election.
Witnesses said riot police and Basij militia members fiercely loyal to Iran's most powerful figure, Supreme Leader Ayatollah Ali Khamenei, were out in force in Tehran on Thursday for the anniversary of student protests in 1999, in which one student was killed.
"Police do not even allow formation of small groups," one witness said.