Kabul, Afghanistan (CNN) -- Authorities in southwestern Afghanistan have seized 19 tons of explosive devices that had been transferred across the border from Iran, police said.

Nimruz Police Chief Abdul Jabar Purdel said a suspect was detained. Nimruz province, in Afghanistan's southwestern corner, borders Iran and Pakistan

The devices had been placed in 337 boxes inside a 40-foot shipping container transferred from Iran over a bridge linking Afghanistan and Iran, he said.

Earlier this year, a senior U.S. Defense Department official said that new U.S. military intelligence suggests Iran planned to smuggle new shipments of weapons into Afghanistan as part of an increased effort to interfere with coalition operations.

The information came from an "Iranian source" whose tips on past shipments have been verified by the United States, the official said in April.

The official also noted that Iran -- a majority Shiite country -- and the Sunni Taliban almost went to war with one another in the late 1990s, so it's not really in their interest to be a major source of top-shelf arms to the Taliban.

Tehran has consistently denied supporting groups opposed to the Afghan government. U.S. and coalition troops have found evidence of some Iranian weapons inside Afghanistan in seized caches or in the aftermath of attacks.