NATO forces in Afghanistan have seized 48 Iranian-made rockets intended to aid the Taliban's spring battle campaign, the most powerful illicit weapons ever intercepted en route from the neighboring state, officials said Wednesday.

The shipment is seen as a serious escalation in Iran's state support of the Taliban insurgency, according to NATO officials and described in detail by an international intelligence official.

It's also an escalation in the proxy war Western officials say Iran is waging against U.S. and other Western forces in Afghanistan, as Washington continues to lobby for tougher international sanctions against Tehran to dissuade it from its alleged goal of building nuclear weapons.

The intercepted 122-millimeter rockets can be fired up to 13 miles (22 kilometers) away from a target, and explode in a burst up to 80 feet (25 meters) wide — double that of the previous 107-millimeter rockets provided by Iran to the Taliban since 2006, the intelligence official said. The official spoke on condition of anonymity to discuss classified matters.

The rockets, which were shown to an Associated Press reporter, were machined without Iranian markings or any serial numbers, but the official says their technical details match other Iranian models. So far, there is no evidence that the 122-millimeter rockets have been used in Afghanistan, though the Taliban has sometimes used Chinese- and Russian-made rockets of the same range in the fight here, harvested from the multiple weapons caches around the country from Afghanistan's decades of civil war.

Iran, which was a staunch opponent of the Taliban when it ruled Afghanistan before the U.S.-led invasion triggered by the Sept. 11, 2001, attacks, has denied allegations that it is supporting militants in the wartorn country.