Iranian security forces have killed at least 18 drug smugglers and armed men near the border with Afghanistan, the latest such incident in the area this month, Iranian media said.

The semi-official Fars News Agency said the clash occurred yesterday in northeastern Iran and that 24 people were killed.

Iranian state television, which had a lower death toll of 18, showed footage of what it said were the dead gunmen lying on the ground in a hilly area.

The men were reportedly killed near the city of Taibad in Khorasan Razavi province, where state media last week said security forces killed 12 drug traffickers and seized 500 kg of narcotics in two operations.

Iran is on the heroin smuggling route to the West from Afghanistan, the world's number one producer of the opium poppy which is the key ingredient for heroin.

Tehran has often accused the United States, its old foe, of failing to combat the growing drugs problem in Afghanistan after US-led forces ousted the Islamist Taliban government in 2001.

Security officials in Afghanistan say resurgent Taliban militants, who have vowed to step up their campaign to expel foreign forces, profit from the trade.

More than 3,300 Iranian security personnel have been killed fighting drug smugglers since Iran's 1979 Islamic revolution.