Reporting from Tehran and Beirut — Violent clashes erupted Thursday in downtown Tehran between thousands of defiant protesters chanting “Death to the dictator” and security forces wielding truncheons, as the political crisis over Iran’s disputed presidential election stretched into its fourth week. Contingents of uniformed and plainclothes security forces flooded the city’s central squares and managed with batons and tear gas to eventually disperse the demonstrators, many of whom wore black and held up their fingers in V-for-victory salutes. Demonstrators in and around Enghelab (Revolution) Square set fire to trash bins to ward off the effects of the tear gas, witnesses said, but mostly avoided engaging security forces in the rock throwing and running street battles that characterized the protests held just after the June 12 election. There were reports of clashes in other Iranian cities, but they could not be confirmed. Demonstrators said they were determined to defy the authorities, led by supreme leader Ayatollah Ali Khamenei, who have demanded an end to rallies and acts of civil disobedience. Tracts distributed online and as leaflets called on protesters to borrow the nonviolent tactics of the U.S. civil rights movement, avoid rifts within their ranks and do nothing that would hamper morale.