(CNN) -- Afghan National Police have seized a stockpile of Iranian-made weapons in the western Afghan city of Herat, a senior U.S. military official confirmed to CNN Thursday.
The official asked not to be identified because of the sensitive nature of the intelligence surrounding Iran's involvement in Afghanistan.
The city of Herat is located in the province of the same name and lies close to Afghanistan's western border with Iran. The area has been relatively peaceful in recent months.
In the past, U.S. troops have discovered small numbers of Iranian-made weapons they believe came across that border but were shipped to insurgents in southern Afghanistan.
The cache, which was discovered August 27, includes a number of weapons and explosive components the United States believes were recently manufactured and smuggled into Afghanistan with the support of Iran's Al-Quds force, the official said.
"We believe the al-Quds force is still trying to destabilize Afghanistan," he said.
At the Pentagon daily briefing Wednesday in Washington, spokesman Geoff Morrell responded to a question about Iran's influence in Afghanistan, saying that Tehran is both helpful and unhelpful.
"They are neighbors and trade partners and have cultural and economic ties, in some cases religious ties, as well," Morrell said.
"But Afghanistan is not immune from Iranian meddling or from Iranian munitions showing up," he said, speaking of past incidents. "But it is most acutely a problem in Iraq."
Included in the stockpile were a number of explosives weapons, roadside bombs that are particularly manufactured in Iran to be able to penetrate armored vehicles, as well as Iranian-made 107mm rockets, firing devices and C-4 plastic explosives.
The official could not confirm the specific number of items seized but said all the material appeared to be in "very good, new condition" and much of it had Iranian manufacturing markings.
The official also confirmed that on August 17, an Iranian-made 107mm rocket was fired at U.S. troops just south of Herat.