Separately, UN says mortar fire targeting aid distribution kills four relief workers and seven civilians in 48 hours.

Three suicide car bombs driven by ISIL fighters killed at least 15 civilians and eight Iraqi policemen on Thursday in an eastern suburb of Mosul, a military statement said.

The attacks targeted Kokjali, a suburb that authorities said they had retaken from ISIL almost two months ago. A military spokesman told Reuters news agency the vehicle bombs went off in a market.

Meanwhile, mortar fire killed 11 people – including four aid workers – as civilians gathered to receive assistance in the war-torn city of Mosul, the United Nations said on Thursday.

READ MORE: Battle for Mosul – ‘I miss everything there’

Iraqi forces launched an operation on October 17 to retake Mosul – the country’s last city held by the Islamic State of Iraq and the Levant (ISIL) – and have retaken part of its eastern edge. But these areas are still exposed to deadly artillery attacks, suicide vehicle bombings, and sporadic gunfire.

“According to initial reports, four aid workers and at least seven civilians queueing for emergency assistance in eastern Mosul city have been killed by indiscriminate mortar fire,” Lise Grande, UN humanitarian coordinator in Iraq, said in a statement.

“Within the last 48 hours, there have been two separate incidents” which also wounded as many as 40 people, she said.

Mahmud al-Sorchi, a spokesman for volunteer fighters from Nineveh province, of which Mosul is the capital, said mortar fire killed aid workers from a local organisation called Faz3a.

The UN’s Damian Rance told Al Jazeera it was still unknown who targeted the aid workers and civilians. But he said ISIL combatants retreating from the military offensive have repeatedly shelled areas after they were retaken by the army, killing or wounding scores of residents fleeing in the opposite direction.

“I do not think we will ever know for certain which party fired the mortar rounds on Thursday,” said Rance, a UN communications officer based in Mosul.

READ MORE: Battle for Mosul – ISIL’s innocent victims

“However, given that Iraqi forces have not been using artillery in Mosul city, and given that it is likely that the mortar rounds came from probable ISIL-held locations, the probability that the mortar rounds were fired by ISIL is high.”

Mosul’s civilians are increasingly being caught in the crossfire, Human Rights Watch said in a statement on Wednesday.

More than 100,000 people have been displaced since the battle for the key city began more than two months ago, but the Iraqi government has encouraged civilians to stay in their homes if possible.

This keeps the number of people fleeing from reaching the catastrophic proportions estimated by some aid organisations before the Mosul operation began, but also exposes civilians to significantly more danger than they would face if they moved to camps.