Blast hitting Popular Mobilisation Forces comes amid ongoing attacks on Iran-linked groups as regional tensions soar.

The PMF said “the attack” late on Friday targeted the Kalsu military base, located some 50km (31 miles) south of the capital Baghdad in the province of Babil (Babylon).

Videos and images from the scene showed a huge explosion, which also set fire to trees in the surrounding areas, spreading the blaze. Footage from inside the base on Saturday morning showed a large crater and damage to infrastructure and vehicles.

In a statement, the PMF claimed “American aggression bombed the Kalso military base”, which is located near the town of Iskandariya.

The Iraqi military said on Saturday that there were no drones or fighter jets detected in the airspace of the Babil area before or during the blast. One PMF member was killed and eight injured in the blast, an army statement said.

The United States military denied reports that it was behind air strikes in Iraq.

We are aware of reports claiming that the United States conducted airstrikes in Iraq today. Those reports are not true. The United States has not conducted air strikes in Iraq today.

— U.S. Central Command (@CENTCOM) April 20, 2024

The Iraqi government said it was investigating the incident. Iraq’s Prime Minister Mohammed Shia al-Sudani is currently in the US.

The bases also houses Iraqi federal police and Iraqi military forces.

Reporting from Baghdad, Al Jazeera’s Mahmoud Abdelwahed said the PMF, which is a part of the official security forces of the state of Iraq, described an “indiscriminate” attack.

“Injuries included individuals with the PMF, soldiers with the Iraqi Ministry of Defence, as well as civilians who were in the vicinity of the military site when it was attacked,” he said.

Abdelwahed added that Camp Kalsu was under the control of US soldiers during the US-led invasion of Iraq, but it was handed over to the Defence Ministry in 2011. It has an ammunition depot and a warehouse for tanks and other weaponry.

“All fingers are pointed towards Israel, accusing Israel of carrying out the attack,” he said. There was no comment from the Israeli military.

Abu Fadak al-Muhammadawi, the chief of staff of the PMF, inspected the base on Saturday.

The Islamic Resistance in Iraq, the umbrella group of Iraqi armed forces who are opposed to the US and Israel, said it launched a retaliatory strike in the early hours of Saturday. It released a video that showed a drone being launched at night and claimed it was aimed at a “vital target” in the Israeli port city of Eilat.

The group has launched dozens of attacks on US and Israeli interests across the region after the current conflict in Gaza started in October. But it largely halted its assaults since February after three US soldiers were killed in a drone strike on a base near Syria’s border with Jordan.

Palestinian armed group Hamas in a statement on Saturday “strongly condemned” what it called an attack on the base and said it “considers it a violation of Iraq’s sovereignty”.

Rich Outzen, a fellow at the Atlantic Council, told Al Jazeera that it would be unlikely for the US to have carried out an attack since it has been trying to contain regional tensions between Iran and Israel.

“This attack would be more in line with what Israel has done below the threshold of direct attacks on Iran regionally,” he said.

The blast comes a day after Iran said it shot down three quadcopters over its skies in the central city of Isfahan near a military base where a number of fighter jets and air defence batteries were situated, with no damage or casualties reported.

Israel is believed to be behind the Isfahan operation but has not officially acknowledged it.

On April 13, Iran launched hundreds of drones, along with cruise and ballistic missiles, at Israel, most of which were shot down by an air defence coalition of Israel, the US, the United Kingdom, France and Jordan.

The Iranian attack was in retaliation for the levelling of Tehran’s consulate building in Syria earlier this month which killed members of the Islamic Revolutionary Guard Corps (IRGC), including two generals.