Three bombs went off in and around Baghdad on Monday, killing at least 14 people, including Shi’ite Muslim worshippers conducting an annual pilgrimage inside the capital, police and medical sources said.

The largest blast resulted from an explosives-laden car parked in the Saydiya district of southern Baghdad that killed 11 and wounded 30, sources said. ISIS claimed responsibility for the attack in an online statement. It said the assault was carried out by a suicide bomber, but Iraqi officials denied that.

Tens of thousands of Shiite faithful have been making their way this week to the northern Baghdad neighborhood of Kadhimiyah, where Imam Moussa al-Kadhim is buried, a great-grandson of Prophet Mohammad who died in the 8th century. Security forces have blocked major roads in Baghdad in anticipation of attacks against pilgrims who traditionally travel on foot from different parts of Iraq.

Explosives planted on the ground in Tarmiya, 25 km (15 miles) north of Baghdad, killed two and wounded six, while a roadside bomb in Khalisa, a town 30 km (20 miles) south of the city, left one dead and two wounded. There was no immediate claim of responsibility for the smaller attacks.

Monday’s attack came a day after two car bombs in the southern Iraqi city of Samawah killed at least 31 people and wounded 52, an attack that was also claimed by the ISIS.

ISIS militants fighting Iraqi forces in the north and west regularly target security personnel and Shi’ite civilians whom they consider apostates.

The group said in an online statement distributed by supporters that a suicide bomber had targeted pilgrims in the Dora neighbourhood adjacent to Saydiya. It said the attack was part of an offensive launched recently in apparent retaliation for the killing of a senior leader.

ISIS’s al Qaeda predecessor was blamed in the past for such attacks on Shi’ite pilgrims, including blasts in 2012 that left 70 people dead nationwide.

Security has gradually improved in Baghdad, which was the target of daily bombings a decade ago, but there has been a wave of blasts in recent days.

According to the United Nations, at least 741 Iraqis were killed in April due to ongoing violence, a sharp decline from the previous month (1,119 people were killed and 1,561 wounded in March). In its monthly report issued on Sunday, the U.N. mission to Iraq put the number of civilians killed at 410, while the rest were members of the security forces. A total of 1,374 Iraqis were wounded that month, it added.

Monday’s blasts come as Iraq struggles to emerge from a political crisis over reforming its governing system which saw protesters hold an unprecedented sit-in over the weekend in Baghdad’s heavily-fortified Green Zone.

The annual Shiite pilgrimage prompted anti-government protesters on Sunday to disband their demonstration – at least temporarily – in Baghdad’s heavily fortified Green Zone that they had stormed a day earlier.