TEHRAN, Iran (CNN) -- Security forces in Iran on Thursday confronted thousands of protesting Iranians across the city, first at a cemetery and later at a prayer venue and near a government building, witnesses and news reports said.





Mourners gather around the grave of Neda Agh-Soltan in Beheshte Zahra Cemetery.





Clashes erupted at the cemetery as two of Iran's main opposition leaders tried to join the several thousand people at a memorial for the slain woman who became the symbol of Iran's post-election violence, witnesses said.





The gathering was banned, but participants ignored the government strictures.





However, security forces barred opposition leaders Mir Hossein Moussavi and Mehdi Karrubi from the gravesite of Neda Agha-Soltan, the 26-year-old woman shot in election protests on June 20, witnesses and news reports said.





More than 3,000 people were gathered at Agha-Soltan's grave, a witness said.





Mourners arrived on the religiously significant 40th day after the fatal shooting in Tehran. For Iranians, a predominantly Shiite Muslim population, the 40th day after a death marks the last official day of mourning.





At the cemetery, security forces used tear gas to clear the area of demonstrators and mourners. A witness said riot police and Basij militia were at the scene, but the confrontations with people in the crowd involved the militia.  Watch a report on the memorial clashes »





The witness spotted instances of the baton-wielding militia charging the gathering, and said as many as nine beatings were seen. Other people  appeared to have been beaten as they ran from police, the witness said. One of the mourners had a bloody head and one woman said she was struck on the back of the neck.





One security force member sustained some sort of injury to the head and was bloodied. It is unclear exactly how that person was injured.





A confrontation between women protesters and police also was seen. The women shouted, "Don't beat up our young people. You, our Muslim brothers. It is a shame to beat up our young people."





The crowd chanted "Ya Hossein, Mir Hossein," the first a reference to the revered Shiite imam and the second a reference to Moussavi. Then there were more chants of "Allah wa Akbar," or God is great. iReport.com: Share your photos, video, stories





Despite reports of arrests, none were seen on the mourning day.





U.S. State Department spokesman Ian Kelly said using force to "break up a group of people who were trying to exercise an important ritual in Islam, the mourning after 40 days," was "particularly disturbing."





"We stand by the Iranian people who are exercising their universal right to self-expression and demonstrating peacefully," Kelly said.





Iran's state-run news agency, IRNA, reported that the mourners "disrupted the order" in the city and damaged public and private property and that security forces were merely trying to control the "illegal activity" of the group.





IRNA also reported that Tehran residents in the area were angry with the constant protests and wanted a stronger response from the security forces.





Another witness told CNN that police directing traffic at the cemetery were helpful and friendly, in stark contrast to the riot police and Revolutionary Guard members who were at the gravesites.





From the cemetery, the mourners arrived at the Mossalla, a building under construction that is expected to be the main venue of Tehran's Friday prayers, witnesses said. A couple thousand people demonstrated and police worked to disperse the crowd -- which also was defying a ban on such a gathering.





"The police tried to discourage drivers from driving the main highway that would lead to central Tehran, but very few listened," one witness said. "Soldiers standing along the streets flashed the peace sign back at the honking cars with large smiles on their faces. It was obvious the soldiers and police forces were with the people."





Thousands also marched and chanted along a prominent thoroughfare called Vali Asr Street, chanting slogans such as "Death to the dictator" amid the honking of car
How many mourners gathered at the grave site? Who was shot in street protests after election on June 20? What did security forces do? Where did forces confront protesters?
More than 3,000 Neda Agha-Soltan, confronted thousands of protesting Iranians across the city,
question: How many mourners gathered at the grave site?, answer: More than 3,000 | question: Who was shot in street protests after election on June 20?, answer: Neda Agha-Soltan, | question: What did security forces do?, answer: confronted thousands of protesting Iranians | question: Where did forces confront protesters?, answer: across the city,