Demonstrators have hit the streets since early October in Baghdad and the Shiite-majority south to demand the ouster of a government they accuse of being corrupt, inefficient and beholden to foreign powers.

After a spike in deaths this week raised the toll to more than 420 killed, Prime Minister Adel Abdel Mahdi said Friday he would submit his resignation to parliament. The chamber was due to convene later Sunday, but no agenda had yet been published.

In recent weeks, most Sunni-majority areas refrained from protesting, fearing that opposing the central government would earn them the labels of being "terrorists" or supporters of ex-dictator Saddam Hussein.

But after a spike in violence days ago left nearly 70 people dead across three cities, Iraqis in nearly all provinces turned out in solidarity.

In Sunday's marches, hundreds of students dressed in black organised a mourning march in the northern city of Mosul, on the city's university campus.

"It's the least Mosul can give to the martyrs of Dhi Qar and Najaf," said Zahraa Ahmed, a dentistry student, naming the two provinces where most recent victims were from.

"The protesters are asking for their basic rights so the government should have answered from the beginning."

Another student, Hussein Kheder, carrying an Iraqi flag, said the whole country was now on the same page politically.

"Now the government needs to answer to the protesters' demands," he told AFP.

For three years, Mosul was the heart of the Islamic State group's ultra-conservative "caliphate", and much of it still lies in ruins today.

In Salahaddin, another northern Sunni province where no rallies had taken place so far, authorities had already declared on Friday three days of mourning for the victims.

And eight other Shiite-majority provinces have announced on Sunday a mourning day during which government offices would remain shut.

More than 20 people were killed in the shrine city of Najaf, 40 people in the hotspot of Nasiriyah and three in the capital Baghdad.

AFP's correspondent reported calm in Nasiriyah on Sunday after three consecutive days of violence.

The protest hotspot is the birthplace of Abdel Mahdi, the embattled premier, who came to power just a year ago based on a shaky alliance between rival parties.

He had resisted protesters' calls for him to step down over the past two months.

But the crackdown turned the tide this week, as it prompted Iraq's top cleric Grand Ayatollah Ali Sistani to call on parliament to drop its support for Abdel Mahdi.

In quick succession, political factions indicated they would support a no-confidence vote.

It was however not certain whether that vote would take place Sunday afternoon as no agenda had yet been published.