Weapons, vehicles and equipment worth more than $500 million that the United States gave to Yemen to help them fight terrorism has gone missing.

Officials fear that the military hardware - thought to include 160 Humvees, four Heuy II helicopters, four hand-launched drones, two Cessna aircraft, a specialist surveillance aircraft and four patrol boats - may have fallen into the hands of an Iranian-backed militia or al-Qaeda.

Small arms and other equipment, such as M-4 assault rifles, Glock 9mm pistols, body armour, pairs of night vision goggles and 1.25 million of rounds of ammunition, may also have vanished.

Missing: U.S. firearms supplied to the Interior Ministry in Yemen, many of which may have gone astray

Violent: Members of the Houthi militia walk in front of the scene of a drive-by shooting in which one Houthi official was killed

The hardware has gone missing since 2007. The Pentagon has now suspended several other packages of military aid to the country.

Requests from Yemen for heavy weapons, including fast jets, tanks and artillery, have also been rejected.

Keeping track of military aid has become more difficult since the U.S. closed its embassy in the capital Sana'a in February after the city fell into the hands of Shia rebels, according to the Washington Post.

Yemen's government was ousted by Shiite rebels who are supported by Iran.

The Houthi rebels have seized many buildings around the capital and in the northern part of the country.

President Obama tasked US military advisers to train Yemeni anti-terror forces.

The US began shipping military aid to Yemen in 2007.

It is feared that some of this weaponry may have been looted by powerful families in Yemen but much of it is feared to have made its way to Jihadis.

Meanwhile, the Houthi rebel group, which has been in control of Sana'a since September, has released members of the government from house arrest.

Horror: A Yemeni boy stands next to bloods stains at the site where Abdul Karim al-Khiwani, a member of the Revolutionary Committee of the Huthis who control Sanaa, was shot dead

Violence continues to plague the country.

This week, one of Yemen's top journalists and activists close to the Houthi militia, Abdul Kareem al-Khaiwani, was gunned down by motorcyclists in front of his son, according to the group's official television channel al-Maseerah.