BAGHDAD: Three ISIS suicide bombers targeted a police base in Iraq’s western Anbar province with explosives-laden Humvees Monday, killing at least 41 police and Shiite militiamen, officials said.

The attack on a police station in the Tharthar area north of the ISIS-held provincial capital, Ramadi, caused a large secondary explosion in an ammunition depot, the officials said. Another 63 security forces members were wounded in the attack.

Hospital officials confirmed the casualties. All officials spoke on condition of anonymity because they are not authorized to brief the media.

Monday’s attack resembled the massive, coordinated assault launched on Ramadi last month that allowed ISIS militants to capture the city, marking their biggest gain since a U.S.-led coalition began launching airstrikes against the extremist group last August. In that assault, the ISIS group also used Humvees looted from Iraqi security forces.

The loss of Ramadi prompted Iraqi Prime Minister Haider al-Abadi to order Shiite militiamen into the vast, Sunni-majority province, which was an insurgent hotbed during the eight-year U.S. military presence.

The Shiite militiamen have played a key role in pushing ISIS back elsewhere in Iraq, but have also been accused by rights groups of carrying out revenge attacks against Sunni citizens, charges denied by militia commanders.

Also, an Iranian officer was killed near Ramadi while advising Iraqi forces on how to recapture it from ISIS, Iranian state media reported.

Jassem Nouri, who had also served as a military adviser in Syria, was killed Thursday, Iran’s official IRNA news agency reported.

Political and military leaders joined family members for a memorial service in Ahvaz in southwestern Iran Sunday ahead of his burial Monday.

“A seasoned (1980-88) Iran-Iraq war commander, Jassem Nouri was there as a military adviser to share his experience with the resistance fighters in Iraq,” the city’s Friday prayer leader Qassem Khaziravi told mourners.

Meanwhile, the U.N. mission to Iraq said Monday that more than 1,031 people were killed and another 1,648 were wounded in violence across the country last month.

The U.N. figures showed that 665 civilians and 366 members of the Iraqi security forces were killed in May. Baghdad was the worst affected province with 343 killed and 701 wounded. But, the UNAMI statement excluded deaths from ongoing fighting in Anbar, due to problems in verifying the “status of those killed.” The figures also leave out insurgent deaths.

In announcing the latest casualty figures, the U.N. mission said that military action alone is not enough to defeat ISIS and called for a power-sharing among Iraq’s ethnic and sectarian groups.

“For any military gains to be sustainable, the government of Iraq must adopt a set of confidence-building measures toward disaffected communities, enabling them to assume a share in governing their matters,” said Jan Kubis, the United Nations secretary-general’s special representative for Iraq.