At least 21 people, including Shia pilgrims, were killed in three suicide bombings in northern Iraq.

Islamic State of Iraq and the Levant (ISIL, also known as ISIS) fighters have claimed responsibility for several suicide bombings that have killed at least 21 people and wounded dozens in two cities in northern Iraq.

The deadly attacks came as Iraqi government forces battled ISIL fighters to retake Mosul, Iraq’s second largest city.

READ MORE: Iraq – Can Mosul survive ISIL?

The attacks in the cities of Tikrit and Samarra on Sunday appeared to be part of a series of diversionary attacks by the armed group.

ISIL issued a statement claiming the attacks, and said that there were three suicide bombers: two who struck Shia pilgrims in the town of Samarra,95 kilometers north of Baghdad, and the third who attacked Tikrit.

At least four Iranians killed

Sunday’s deadliest attack took place in the city of Samarra, which is home to a major Shia shrine.

Local officials said an attacker set off a bomb-packed ambulance in a parking lot near Shia pilgrims before a second suicide bomber detonated his explosives vest.

The attack killed 11 people, including at least four Iranians, and wounded up to 100 other people.

Another suicide attacker rammed an explosives-laden car into a busy checkpoint outside the city of Tikrit, killing at least nine people.

ISIL claimed both attacks.

Smaller bombings in Baghdad

In the capital, Baghdad, a series of smaller bombings killed at least 10 people and wounded 21 others, according to police and medical officials, who spoke to AP news agency on condition of anonymity because they were not authorised to brief reporters.

No one immediately claimed the attacks, but they bore the hallmarks of ISIL.

The attacks in Iraq on Sunday came as thousands of troops attempted to capture the ISIL-held city of Mosul, some 400 kilometres to the south.

Mosul is the only major Iraqi city still held by Islamic State of Iraq and the Levant, also known as ISIS, which seized control of the city in 2014.

Last month, Iraqi troops and special forces, Shia militias, Kurdish Peshmerga fighters, and other groups backed by US-led air raids launched a campaign to retake the city.

Another wave of attacks were carried out in Baghdad by the group earlier this month, ending a brief lull of violence in the city. In total, including Sunday’s blasts, more than 100 people have been killed overall in October.

The last major attack, on October 16, was the deadliest to hit the Iraqi capital since early July, when a suicide bombing in central Baghdad sparked fires in a crowded shopping area, killing more than 300 people.