BGM-71 TOW, variant M220, SABER. U.S. Army PFC David Mitchell scans the landscape surrounding Vehicle Patrol Base Badel at the mouth of the Narang Valley in Konar province, Afghanistan, May 9, 2009. Mitchell is assigned to the 1st Battalion, 32nd Infantry Regiment. The base has closed down enemy activity in the valley and in Narang, Chowkay and Nurgal districts. US Army Some Syrian rebel groups are being armed with advanced American-made antitank missiles in a test run to judge whether the arms end up in the hands of extremist groups in the region, The Wall Street Journal reports.

With Saudi assistance, the U.S. has delivered about a dozen BGM-71 TOW (Tube-launched, Optically-tracked, Wire-guided) missile systems to at least one rebel group.

"To make it clear, our allies are only delivering these missiles to trusted groups that are moderate," one senior leader of rebel group Harakat Hazm told WSJ. "The first step is showing that we can effectively use the TOWs, and hopefully the second one will be using antiaircraft missiles."

The TOW, first introduced in 1970, is a very effective weapon system that can take out tanks, other heavily-armored vehicles, and bunkers. It can be fired in a ground role on a tripod, or mounted to a vehicle.

This marks a big shift in the policy of the U.S. toward Syrian rebel groups fighting Assad forces, as so many disparate factions blur the spectrum from freedom fighter to hardline extremist. While the U.S. had already been supplying small arms such as rifles to vetted rebel groups, advanced weaponry such as antitank and antiaircraft weaponry would considerably level the playing field.

Meanwhile, Russia has been supplying the Assad regime with advanced weaponry for quite some time.

The CIA and special operations forces have also been training rebel groups in two-week courses at a U.S. base in southwest Jordan.