Iraq's powerful cleric Muqtada al-Sadr ordered his followers to end their protests in central Baghdad on Tuesday and apologized to Iraqis after deadly clashes between rival Shiite Muslim groups.

"This is not a revolution because it has lost its peaceful character," Sadr said. "The spilling of Iraqi blood is forbidden."

In a televised address delivered at 1 p.m. (10 a.m. GMT), Sadr set a one-hour deadline for his supporters to leave their protests in the fortified Green Zone in central Baghdad, where they have occupied parliament for weeks.

"Within 60 minutes, if the Sadrist Movement does not withdraw, including from the sit-in at parliament, then even I will leave the movement," Sadr said.

His address came a day after the worst violence in the Iraqi capital in years – which follows a 10-month political deadlock since October's parliamentary election – prompted neighboring Iran to close its border and halt flights to Iraq.

Supporters of al-Sadr fired rocket-propelled grenades and machine guns into Iraq's Green Zone as security forces returned fire earlier Tuesday, seriously escalating a monthslong political crisis gripping the nation.

Baghdad's streets were mostly empty on Tuesday. Gunmen cruised in pickup trucks carrying machine guns and brandishing grenade launchers, but residents observed a curfew. Overnight, sustained gun and rocket fire rang out across the city.

The death toll rose to at least 30 people after two days of unrest, officials said.

Monday's violence was prompted by al-Sadr's announcement that he would withdraw from all political activity – a decision he said was in response to the failure of other Shiite leaders and parties to reform a corrupt and decaying governing system.

Those backing cleric al-Sadr earlier stormed the Green Zone, once the stronghold of the United States military that's now home to Iraqi government offices and foreign embassies. At least one country evacuated its diplomatic personnel amid the chaos.

Iraq’s government has been deadlocked since al-Sadr’s party won the largest share of seats in October parliamentary elections but not enough to secure a majority government – unleashing months of infighting between different Shiite factions. Al-Sadr refused to negotiate with his Iran-backed Shiite rivals, and his withdrawal Monday has catapulted Iraq into political uncertainty and volatility with no clear path out.

Iran closes border

The violence threatened to deepen the political crisis, though streets elsewhere in the country largely remained calm and the country's vital oil continued to flow. Neighboring Iran closed off its borders to Iraq and urged its citizens to avoid traveling there, a senior official said, a sign of Tehran's concern that the chaos could spread.

Iran's state television said flights had also been halted "until further notice because of the unrest there."

Millions of Iranians travel to the Iraqi city of Karbala every year for the ritual of Arbaeen, which marks the end of a 40-day mourning period for the grandson of the Prophet Muhammad, Imam Hussein. Arbaeen falls on Sept. 16-17 this year.

"The border with Iraq has been closed. Due to safety concerns, it is necessary for Iranians to refrain from travelling to Iraq until further notice," state TV quoted Iran's deputy Interior Minister Majid Mirahmadi as saying.

Live television footage showed supporters of al-Sadr firing both heavy machine guns and rocket-propelled grenades into the heavily fortified Green Zone through a section of pulled-down concrete walls. Bystanders, seemingly oblivious to the danger, filmed the gunfight with their mobile phones.

As al-Sadr's forces fired, a line of armored tanks stood on the other side of the barriers that surround the Green Zone. Heavy black smoke at one point rose over the area, visible from kilometers (miles) away.

At least one wounded man was taken away in a three-wheel rickshaw, the Iraqi Foreign Ministry visible in the background.

At least 30 people have been killed and over 400 wounded, two Iraqi medical officials said. The toll included both al-Sadr loyalists killed in protests the day before and clashes overnight. Those figures are expected to rise, said the officials, who spoke on condition of anonymity because they weren’t authorized to release the information to journalists.

Members of Iraq's Shiite Muslim sect were oppressed when Saddam Hussein ruled the country, but the U.S.-led invasion reversed the political order. Now the Shiites are fighting among themselves, with Iranian-backed Shiites and Iraqi nationalist Shiites jockeying for power, influence and state resources.

Al-Sadr’s nationalist rhetoric and reform agenda resonates powerfully with his supporters, who largely hail from Iraq’s poorest sectors of society and were historically been shut out from the political system under Saddam.

His announcement that he is leaving politics has implicitly given his supporters the freedom to act as they see fit.

Iranian state television cited unrest and a military-imposed curfew in Iraqi cities for the reason for the border closures. It urged Iranians to avoid any travel to the neighboring country. The decision came as millions were preparing to visit Iraq for an annual pilgrimage to Shiite sites, and Tehran encouraged any Iranian pilgrims already in Iraq to avoid further travel between cities.

Kuwait, meanwhile, called on its citizens to leave Iraq. The state-run KUNA news agency also encouraged those hoping to travel to Iraq to delay their plans.

The tiny Gulf Arab sheikhdom of Kuwait shares a 254-kilometer- (158-mile-) long border with Iraq.

The Netherlands evacuated its embassy in the Green Zone, Foreign Affairs Minister Wopke Hoekstra tweeted early Tuesday.

"There are firefights around the embassy in Baghdad. Our staff are now working at the German embassy elsewhere in the city," Hoekstra wrote.

Dubai's long-haul carrier Emirates stopped flights to Baghdad on Tuesday over the ongoing unrest. The carrier said that it was "monitoring the situation closely." It did not say when flights would resume.

On Monday, protesters loyal to al-Sadr pulled down the cement barriers outside the government palace with ropes and breached the palace gates. Many rushed into the lavish salons and marbled halls of the palace, a key meeting place for Iraqi heads of state and foreign dignitaries.

Iraq’s military announced a nationwide curfew, and the caretaker premier suspended Cabinet sessions in response to the violence.