From the L.A. Times:

Reporting from Tehran and Beirut — Thousands and possibly tens of thousands of mourners, many of them black-clad young women carrying roses, overwhelmed security forces today at Tehran's largest cemetery to gather around the grave of Neda Agha-Soltan, the young woman whose videotaped shooting at a June 20 demonstration stunned the world.

According to one witness, who asked not to be identified for fear of reprisal, Mousavi stepped out of his car only to be surrounded by police, who forced him back into his vehicle and out of the cemetery.

At first, mourners were confronted by security forces, who struck some with batons and made arrests in an attempt to bar them from gathering at Tehran's Behesht Zahra cemetery, the country's largest. The tree-lined streets leading to the graves of Agha-Soltan and others were blocked by riot police, the witness said.

The witness said protesters identified and violently confronted several plainclothes Basiji militiamen.

"Police, police, support us," the crowd chanted. "God is great!"

Among those arrested was award-winning director Jafar Panahi, whose movies "The Circle" and "Crimson Gold" have garnered international acclaim, along with his wife and daughter, a source close to the family told Agence France-Presse.

But as people poured out of the nearby subway station and taxis along the highway, security forces retreated. One witness said police released detainees and began cooperating with the mourners, directing them to Section 257 of the cemetery, where Agha-Soltan and others were buried.

This video, from a Farsi site linked by the New York Times, purportedly shows the cemetery protests:

Meanwhile in D.C., a bipartisan "raft of senior senators" continues to press Obama to levy sanctions against Iran.