Lebanon’s Hezbollah militant group, recognized as terrorist organization by the US, has been allegedly spotted parading a vast number of US-made military vehicles in Syria, triggering questions about how they ended up in the militants’ hands.

The photos of Hezbollah’s military parade allegedly featuring US-made armored vehicles in the Syrian city of Qusayr published by media close to the organization raised questions the US State Department had to confront during a daily press briefing on Tuesday.

“Our embassy in Beirut is working with the Lebanese armed forces to investigate the images circulating on social media purporting to show Hezbollah displaying US military equipment in Syria,” State Department spokeswoman Elizabeth Trudeau said.

She added that there was “no information on them [the images],” but the US would be “gravely concerned if equipment ended up in the hands of Hezbollah.”

The US equipment on the photos appear to be the M113 armored personnel carriers that have been in service since 1960 and “are extremely common in the region,” Trudeau noted.

The State Department spokeswoman also noted that “the Lebanese military has publicly stated that the M113s depicted online in the Hezbollah military parade were never part of their equipment roster.”

“The photos of vehicles circulated by media outlets were not taken from the army and do not belong to the military,” the Lebanese army said in a statement.

Hezbollah’s vehicles seen during the parade also showcase Russian tanks.

Charles Shoebridge, a security analyst and former UK counter-terrorism intelligence officer, in an interview with RT compared the M113 tank to the “Kalashnikov of the personnel carrier world,” adding that the Lebanese Army was the most probable source of the equipment.

“Certainly the finger would seem to point… at the Lebanese Army, because many of them [the APCs] were supplied to them,” Shoebridge said.

The large number of items of an identical type seen on the photos may suggest that there was “some kind of an organized transfer,” Shoebridge said.

This is not the first time the US weapons and pieces of military equipment allegedly end up in the wrong hands, with a number of reports saying that Al-Nusra and IS (Islamic State) had come into possession of American missiles and other types of weaponry intended for so-called moderate opposition groups in Iraq and Syria.

Moderate opposition militants tend to defect with the US weapons, join terrorist organizations and use it against the US troops, Shoebridge added.

“This policy of supplying rebel groups with sophisticated weaponry or any weaponry invariably seems to backfire,” he concluded.