BAGHDAD — A drone strike caused a massive explosion last week at a munitions depot run by an Iranian-backed militia near Iraq’s capital, Baghdad, according to an Iraqi government report obtained Wednesday.

The document shows that a government investigation concluded a drone had set off the blast.

The finding deepens the question of who is behind a string of at least three mysterious explosions that have hit militia bases in Iraq over the past month. Speculation among media and officials has ranged among a number of possible perpetrators, including Israel, Islamic State militants, the United States or rival Iraqi factions.

The Associated Press on Wednesday obtained the report outlining the conclusions of a fact-finding committee ordered by the government to investigate the Aug. 12 explosion at the al-Saqr military base.

It said the blast was caused by a drone strike that sparked a huge fire and ruled out earlier suggestions that it was caused by an electrical short circuit or faulty storage of munitions that allowed them to overheat in sweltering summer temperatures.

The report did not say who the drone belonged to.

The blast at al-Saqr, or "Falcon," base killed one civilian, wounded 28 and damaged nearby homes, echoing across Baghdad. The base houses a weapons depot for the Iraqi federal police and the mainly Shiite militias known as the Popular Mobilization Forces. The state-sanctioned militias, most of which receive backing from Iran, have fought alongside Iraq's regular armed forces against the Islamic State group.

Al-Saqr was among a string of explosions that hit militia bases and munitions depots over the past several weeks. The deadliest, a July 19 blast, was blamed on a drone that hit a base in Amirli, northern Iraq, killing two Iranians and causing a huge fire. The most recent explosion came on Tuesday night, at a base north of Baghdad.

Following a national security meeting last week, Iraqi Prime Minister Adel Abdul-Mahdi ordered a ban on all military flights throughout the country — including by members of the U.S.-led coalition in Iraq — unless specifically authorized by the Defense Ministry.

The blasts have given rise to a host of theories, including that Israel may be behind them. The Iraqi government has not formally addressed the reports. The United States has denied any role in the blasts.

If Israel did carry out the bombings, it would be an expansion of its campaign against Iran's spreading influence in the region. Israel has struck Iranian bases in neighboring Syria on numerous occasions, but it is not known to have done so in Iraq.

Asked about the mounting speculation that Israel was striking in Iraq, Israeli Prime Minister Benjamin Netanyahu on Monday said: "Iran has no immunity, anywhere ... We will act — and currently are acting — against them, wherever it is necessary."

He spoke during a visit to Ukraine and was quoted in the Times of Israel.

An American official said the U.S. has no evidence or credible intelligence that Israel was behind the two most recent blasts — on Tuesday or on Aug. 12. The official spoke on condition of anonymity because he was not authorized to speak about the issue.

Associated Press writer Lolita C. Baldor in Washington contributed to this report.