Shiite cleric Muqtada al-Sadr threatened Tuesday to lift a seven-month freeze on his Mahdi Army militia if the Iraqi government does not halt attacks on his followers or set a timetable for a U.S. withdrawal, according to AP. Al-Sadr also called off a mass march that had been planned for Wednesday in Baghdad after hundreds of followers in Shiite areas south of Baghdad complained that Iraqi security forces prevented them from traveling to the capital. The demonstration was supposed to mark the fifth anniversary of the capture of Baghdad by invading U.S. forces. Despite the decision to call it off, the Baghdad military command clamped a vehicle ban on the capital, saying unauthorized cars, trucks and motorcycles would not be allowed on the streets from 5 a.m. to midnight on Wednesday. The announcement was broadcast on Iraqi state TV. Some motorists said they were already being turned back at checkpoints as tensions were high with fierce clashes continuing in the main Shiite enclave of Sadr City. The developments came as the top U.S. commander in Iraq Gen. David Petraeus called for an open-ended suspension of U.S. troop withdrawals this summer, asserting that an overly rapid withdrawal would jeopardize recent security gains. Petraeus made the remarks as he appeared at a Senate hearing with U.S. Ambassador Ryan Crocker.