Question: Who could have known that sending billions of dollars of advanced US weaponry to unaccountable autocratic regimes in the Middle East might lead to those weapons ending up in the hands of rogue militant groups dedicated to destroying the United States? Answer: Probably just about anyone with basic Middle East political knowledge. In an absolute non-shocker, it has now been revealed the Saudi-led coalition fighting Yemeni rebels may have done just that, and transferred US-made weapons to a militia linked to jihadist group al-Qaeda, in an investigation by CNN.

The US news network published the report on Monday, revealing that US arms have also ended up in the hands of the Iran-backed Houthi militia.

According to the investigation, the Abu Abbas Brigade, a hardline coalition-backed militia, is in possession of US-made armoured vehicles.

The militia's leader Abu Abbas was declared a "terrorist" by the US for allegedly financing the Yemeni chapters of al-Qaeda and the Islamic State group.

In a statement to CNN, a US defence official said an investigation had been launched into the report's findings.

If Riyadh and its main coalition ally the United Arab Emirates have handed out US-bought military gear to third parties it would be in violation of their deals with Washington.

"The security and political chaos in Yemen has created a fertile ground for terrorist and violent activities. It is not weird or unexpected to see al-Qaeda militants using US-made weapons in Yemen. This is the end result of the absence of the strong state and the miscalculated war of the Saudi-led coalition. Obviously, al-Qaeda and the Houthis are mortal enemies while al-Qaeda and the coalition have one thing in common: hostility towards the Houthis. So, the coalition seems to think that arming al-Qaeda to fight the Houthi rebels as a short-term tactic, and that they can cooperate with the US to annihilate al-Qaeda when they need and want." - a Yemeni journalist who asked not to named for fears for his safety

The report also revealed that US-made military vehicles have also wound up in the hands of the Houthis rebels, possibly revealing unknown technology to rival Iran.The coalition reportedly airdropped anti-tank missiles to loyalist militias close to where al-Qaeda was operating at the time.

According to the investigation, at least one IED-resistant vehicle that is in the possession of the Houthis was sold to the UAE in 2014.

"[Vehicles] like these, captured on the battlefield, have been probed by Iranian intelligence," the report said, citing rebel sources.

The Saudi-led coalition intervened in Yemen's conflict in 2015 to repel the Iran-aligned Houthis, while the US has waged a drone war on jihadist groups.

Sana Uqba, a writer with The New Arab focusing on Yemen, said the four-year conflict has created a dangerous political vacuum.

"This chaos has allowed US and British weapons which were initially sold to its Saudi ally to venture into the hands of militia groups in Yemen - and at times used irresponsibly - putting civilians at risk," Uqba said.

"It is absolutely imperative that all arms sales to parties involved in the Yemen conflict come to an immediate end."

The report comes amid growing pressure in the US Congress to end US military support for Riyadh's war in Yemen.

Four years of war in Yemen have killed about 10,000 people and are threatening up to 20 million people with starvation.