Baghdad ? Iran seems to be honoring a commitment to stem the flow of deadly weapons into Iraq, contributing to a more than 50 percent drop in the number of roadside bombs that kill and maim American troops, a U.S. general said Thursday.

The comments by Maj. Gen. James Simmons marked rare U.S. praise for Iranian cooperation in efforts to stabilize Iraq. Washington has repeatedly accused the Islamic Republic of aiding Shiite militias and trying to foil U.S. goals in Iraq.

But it remains unclear why Iran may have decided to choke off the suspected weapons pipeline. One possibility is that Iran – the most populous Shiite nation – is seeking to shore up the struggling government of Prime Minister Nouri al-Maliki, a Shiite, in the belief that it will help Tehran’s long-term interests.

Simmons, a deputy commander of Multinational Corps-Iraq, told reporters that the number of roadside bombs either found or exploded nationwide had fallen from 3,239 in March to 1,560 last month.

The October figure was the lowest since September 2005, he said.

Simmons said the decline included all types of roadside bombs, including highly lethal “explosively formed penetrators” – the signature weapon of Shiite extremists – which can hurl a fist-sized chunk of molten copper through the heaviest armor on U.S. vehicles.

U.S. authorities insist penetrator bombs come from Iran, despite Iranian denials.

Earlier this month, Defense Secretary Robert Gates said Iranians had apparently assured the Iraqi government that it would stop the flow into Iraq of bomb-making materials and other weaponry.

“We believe that the commitments that the Iranians have made appear to be holding up,” Simmons said, adding that Iranian-made weaponry still found in Iraq appeared to have been smuggled in months ago.