Iraqi protesters have stormed and set fire to a provincial government building in the southern city of Basra, despite a curfew imposed by authorities on Thursday to try and quell demonstrations against poor public services and unemployment that have turned violent.

Three protesters were shot dead by security forces, according to a medical and a security official. They spoke on condition of anonymity because they were not authorised to release information.

Iraq’s popular Shia cleric Moqtada al-Sadr called for an urgent parliamentary session to discuss the situation in Basra, Iraq’s second-largest province and home to about 70% of the Opec member’s vast oil reserves.

Twelve civilians have been killed since the start of the month in confrontations between demonstrators and police, according to Iraq’s Independent High Commission for Human Rights, which said another 93 civilians and 18 security force personnel have been injured.

The protests showed no sign of abating by Thursday evening as hundreds of young men took to the streets, shouting: "peaceful, peaceful." Several government buildings have been attacked in the past few days of demonstrations that have spread throughout the city.

In a televised speech, al-Sadr said the parliament session should be held no later than Sunday, and that the prime minister and other officials should either attend the session or resign.

The populist cleric’s supporters won the most seats in national elections held earlier this year, but Iraq’s feuding factions have yet to form a new government. The snowballing protests cast a further shadow on those efforts.

A provincial official with state-run Iraqi Ports Co said authorities closed the vital Um Qasr port on the Persian Gulf on Wednesday evening, fearing sabotage. The official, who spoke on condition of anonymity because he was not authorised to release information, wouldn’t say when operations will resume.

Brig Gen Saad Maan, a spokesman for the interior ministry, announced a curfew in Basra starting at 3pm on Thursday, citing "intelligence reports of possible attacks on government offices". The government has said the protesters’ demands are legitimate, while blaming the violence on saboteurs. The curfew announcement was ignored.

Residents of Basra and other cities in Iraq’s southern Shia heartland have been protesting since July over endemic corruption, soaring joblessness and poor public services. Clashes erupted earlier this week, leaving several civilians and police dead. Prime minister Haider al-Abadi has ordered an investigation into the violence.