BAGHDAD -- An Israeli airstrike on an Iranian weapons depot in Iraq, confirmed by U.S. officials, is threatening to destabilize security in the volatile country struggling to remain neutral in the conflict between Washington and Tehran.

It would be the first known Israeli airstrike in Iraq since 1981, when Israeli warplanes destroyed a nuclear reactor being built by Saddam Hussein, and significantly expands Israel's campaign against Iranian military involvement in the region.

The July 19 attack targeted a base belonging to Iranian-backed paramilitary forces in Amirli in the northern Salaheddin province, and killed two Iranians. The attack was followed by at least two other mysterious explosions at munitions depot near Baghdad belonging to the militias.

No one has claimed responsibility for any of the attacks, which have set back security and stability in the country just as it appeared to be on the path to recovery following a devastating fight against the Islamic State group, and decades of war and conflict before that.

Earlier this week, the deputy head of the Iraqi Shiite militias, known collectively as the Popular Mobilization Forces, openly accused Israeli drones of carrying out the attacks but ultimately blamed Washington for allowing it to happen and threatened strong retaliation for any future attack.

Iraq's government, by contrast, has said it is investigating the attacks and has yet to determine who was behind them, warning against attempts to drag Iraq into any confrontation.

Security analyst Motaz Mohieh said Iraq's weak government will not be able to announce the results of its investigation "because it will constitute an embarrassment" for it.

"These strikes will continue to target the factions associated with Iran cause a threat to Israel and the U.S. presence," he predicted.

The fallout could directly affect the future of thousands of American troops in Iraq, providing ammunition and pretext for hard-line factions who want them to leave.

Significantly, a leading Shiite Muslim cleric followed by some Iraqi militant factions issued a public religious edict, or fatwa, on Friday forbidding the presence of U.S. troops in Iraq following the strikes.

In his fatwa, Iran-based Grand Ayatollah Kazim al-Haeri also urged Iraq's armed forces to "resist and confront the (U.S.) enemy," a call likely to inflame tensions in Iraq.

Former Iraqi Prime Minister Nouri al-Maliki also weighed in, warning of a "strong response" if it is proven Israel was behind the recent airstrikes in Iraq.

In statements issued by his office, he also said if Israel continues to target Iraq, the country "will transform into a battle arena that drags in multiple countries, including Iran."

U.S. forces withdrew from Iraq in 2011, but returned in 2014 at the invitation of the government to help battle IS after it seized vast areas in the north and west of the country, including the second-largest city, Mosul. A U.S.-led coalition provided crucial air support as Iraqi forces regrouped and drove IS out in a costly three-year campaign.

The U.S. maintains about 5,000 troops in Iraq, and some groups say there's no longer a justification for them to be there now that IS has been defeated.

The comments by al-Maliki, who was prime minister for eight years and now heads a Shiite bloc in parliament, follow fiery threats to the U.S. made hours earlier by the powerful Hezbollah Brigades, an Iran-backed militia. In a statement, it held the U.S. responsible for the strikes and said any new attacks will be met with a harsh response.

"Be sure that if the confrontation between us starts, it will only end with your removal from the region once and for all," it said.