Shiite cleric threatens to end militia's cease-fire BAGHDAD, Iraq (CNN) -- Shiite cleric Muqtada al-Sadr is threatening to end the oft-broken, seven-month cease-fire of his Mehdi Army militia, according to a statement from him on a Sadrist Web site. Fighting in al-Sadr's stronghold of Sadr City stretched into its third consecutive day Tuesday as he postponed a large demonstration planned for Wednesday in Baghdad. A three-day effort to disarm people in the Shiite Baghdad neighborhood of Kadhimiya is to begin on Wednesday, an Iraqi military spokesman said. Fighting in eastern Baghdad between U.S. troops and Shiite militiamen -- particularly those from al-Sadr's Mehdi Army -- has intensified in recent days. On Tuesday, U.S. and Iraqi forces and militants squared off for a third day in Baghdad. The cleric's supporters initially said troops were stopping them from attending Wednesday's planned protest against the U.S. presence in the war-ravaged nation. However, according to a statement posted on al-Sadr's Web site, the cleric is postponing the demonstration. It was not immediately clear when the demonstration would be held. Saleh al-Ageili, a spokesman for al-Sadr's parliamentary bloc, said protesters heading to Baghdad from Najaf were being prevented by security forces from taking part in al-Sadr's demonstration. He said the government was restricting the protest to Sadr City, even though the demonstration was planned for a wider area in the capital. Al-Ageili said 200 cars carrying protesters from Najaf to Baghdad were stuck in Hilla, in Babil province. A source from Hilla police said they had received orders from Baghdad to block males between the ages of 12 and 35 from proceeding to Baghdad from Monday at 6 p.m. until Thursday at 6 a.m. The demonstration was to coincide with the anniversary of the fall of the Saddam Hussein regime. The rising tension comes as U.S. Gen. David Petraeus, the top American commander in Iraq, and U.S. Ambassador to Iraq Ryan Crocker are scheduled to begin testifying to Congress about the status of the more than five-year-old Iraqi war. They are expected to address and field questions about the sudden upsurge of conflict in Iraq's Shiite region and the power struggle between Shiite political groups. Watch how all eyes in Washington are on Petraeus » The latest round of Baghdad fighting, which was described as sporadic, occurred in the tightly packed slum of Sadr City, where troops and police have been fighting in Mehdi Army militia strongholds. At least 36 people were killed and 139 were wounded during fighting in Baghdad neighborhoods on Sunday and Monday, an Interior Ministry official said. Eight of the 11 U.S. troops killed in Iraq on Sunday and Monday died in fighting in Baghdad. Militants have been firing rockets, rocket-propelled grenades and mortars at patrols in Sadr City and other neighborhoods, and into the heavily fortified International Zone, the U.S. military said. Fighting erupted in Shiite regions across Iraq after Iraqi Prime Minister Nuri al-Maliki launched a March 25 offensive against "criminals" in the southern city of Basra. That operation sparked fighting across the country between al-Sadr's followers and Iraqi security forces, dominated by the Sadrists' rival group, the Islamic Supreme Council of Iraq. More than 700 people were killed, according to U.N. reports. Watch a view from the front lines in Sadr City » The fighting died down last week after al-Sadr ordered his followers to lay down their arms, a directive spawned by talks he held with Iraqi Shiite lawmakers and Iranian officials in Iran. The Sadrist movement used to be part of the Shiite-dominated United Iraqi Alliance coalition, which includes al-Maliki's Dawa party and the Islamic Supreme Council of Iraq. It helped put al-Maliki in power. But the group bolted from the coalition last year, and six Sadrists left their Cabinet posts because al-Maliki wouldn't set a timeline for U.S. troop withdrawal. The Sadrists are active in parliament, where they have 30 seats. Al-Maliki continued his hard line on the Sadrists on Sunday, when he laid down an ultimatum for al-Sadr to disband his Mehdi Army or see his supporters barred from public office. The Sadrists say any effort to bar them from political participation would be unconstitutional -- and that any decision to disband the Mehdi Army is not the government's to make. Al-Sadr spokesman Salah al-Obeidi said al-Sadr has consulted with Iraq's Shiite clerical leadership "and they refused that." He did not provide details of the talks. E-mail to a friend CNN's Jomana Karadsheh contributed to this report.