Moqtada al-Sadr's supporters fired rocket-propelled grenades into Baghdad's Green Zone as Iraq's political chaos deepened. Meanwhile, Iran closed its land borders to its neighbor and ceased all flights.

Violence in Iraq continued for the second day as militants fired rockets at Baghdad's high-security Green Zone on Tuesday, Iraq's military said.

Earlier, sounds of sustained gunfire and rockets rang through the night.

The violence between rival Shiite Muslim groups has killed more than 20 people since it broke out on Monday. At least 380 people were also injured, a medical source told AFP.

Iraq's military announced a nationwide curfew as gunmen cruised empty streets in pickup trucks carrying machine guns and brandishing grenade launchers

The caretaker premier of Iraq suspended Cabinet sessions.

How the unrest started

The violent confrontation erupted after Moqtada al-Sadr, a powerful cleric and a former anti-US insurgent leader, announced he would resign from politics.

Al-Sadr had won the most seats in the elections last October but failed to form a government after refusing to negotiate with Iran-backed Shi'ite groups to form a government.

Al-Sadr's followers have organized street protests and occupied government buildings to block political activity, which has fueled tensions culminating in the violence since Monday.

His militia numbers in the thousands and has millions of loyal supporters.

The clashes occurred between al-Sadr's supporters and the army and men of the Hashed al-Shaabi, former paramilitaries integrated into the Iraqi forces. These heavily-armed paramilitary groups are trained by Iran.

Neighbors react

Meanwhile, Iran closed its land borders to Iraq and also ceased flights citing "unrests'' and "curfew'' in Iraqi cities.

Neighboring Kuwait also urged its citizens in to leave Iraq. Those planning to travel to the country were advised to delay their plans.

The Dubai-based Emirates airline also stopped flights to Baghdad.