Several blasts hit a position held by Iraqi Shi'ite paramilitaries next to Balad air base north of Baghdad on Tuesday, Iraqi military officials and a source in a paramilitary group said.
Balad base hosts U.S. forces and contractors and is located about 80 km (50 miles) north of Baghdad. An Iraqi Shi'ite militia group known as the Popular Mobilization Forces, which is backed by Iran, is stationed nearby.
The military official said the intended target of the blasts was the militia's position near the base. The paramilitary source said his group's weapons depot was specifically targeted by an aerial bombardment.
The U.S.-led coalition could not immediately be reached for comment.
Iraqi media reported several casualties, but there was no immediate confimation.
Witnesses said the explosions caused stored rockets to fly into nearby orchards and into Balad base itself. Others said the strike was committed using drones.
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Iraq's interior ministry has dispatched large forces to the scene, said to be heavily damaged, and launched an investigation.
Last week, Iraq's interior ministry said a large explosion at an ammunition depot southwest of the capital has injured 13 people, most lightly.
Reports on Iraqi media have not named any state or organization behind the possible attack.
The base houses a weapons depot for the Iraqi federal police and the PMF. The state-sanctioned PMF militias, which also receive backing from Iran, have fought alongside Iraq's regular armed forces against the Islamic State group.
Prime Minister Adel Abdul Mahdi last week ordered all ammunition dumps belonging to the armed forces or paramilitary groups to be moved outside of cities.
He also cancelled all special flight permissions for Iraqi and foreign aircraft, meaning sorties including by the U.S.-led coalition operating against Islamic State militants must be cleared in advance by the prime minister.
Some analysts have suggested the strikes might have been carried out by Israel, which last year signalled that it could attack suspected Iranian military assets in Iraq, as it has done with scores of air strikes in Syria.
"Iraq's air defences have very high capability, but one thing they couldn't detect is an advanced Israeli air attack," said Baghdad-based security analyst Hisham al-Hashimi, who advises the government.
Israeli officials have suggested recently they view Iraq, whose main ally is Israel's regional foe Iran, as more of a threat than in recent years, but have not directly commented on the recent blasts at PMF sites in Iraq.
The U.S. coalition has denied any involvement in the recent explosions.
Last month, London-based Arabic newspaper Asharq Al-Awsat reported Israel has expanded the scope of its anti-Iranian attacks and struck targets in Iraq.
The base was formerly used by the People's Mujahedin of Iran, a militia that fought against the Iranian regime.
Over the past year, an number of strikes targeting the Iranian Revolutionary Guards and the Lebanese militia Hezbollah in Syria were attributed to Israel.
Following last month's report, Israeli defense officials said Iran’s military entrenchment in Iraq poses a threat to Israel, adding that Tehran has shifted the bulk of its deployment of missile systems from Syria to Iraq, which is harder for Israel to attack than Syria was.
According to Israeli intelligence, Iran is currently providing Iraqi militias with missiles that have ranges of 200 to 700 kilometers and are capable of hitting anywhere in Israel. These missiles are more accurate than the ones in Hezbollah’s arsenal, and Iran may use them either to hit Israel directly from northern Iraq or to transfer them as needed to Syria and Lebanon.
The Associated Press contributed to this report.