Iran's border patrol police said it seized more than 11 tonnes of drugs, killing one smuggler, in the "biggest" bust since the 1979 Islamic revolution, media reported on Sunday.
"The biggest drug load busted since the revolution, weighing 11 tonnes, has been seized in Jakigour area in Sistan-Baluchestan," bordering Pakistan, border police chief Brigadier General Hossein Zolfaqari said.
The general, quoted in the media, said "one of the drug traffickers was killed and a number of others wounded but managed to escape to the other side of the border," without elaborating.
Zolfaqari said 10 tonnes were opium and the rest hashish, adding that the bust came in a 36-hour operation.
Iran, which lies on a key transit route for narcotics headed for Europe and the Middle East, has seized more than 350 tonnes of drugs, mostly opium, since the start of 2012, according to official figures.
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Three border guards were killed in October during an operation in Sistan-Baluchestan.
More than 4,000 police officers and soldiers have been killed over the past three decades in clashes with traffickers, who often travel in heavily armed convoys, according to officials.
Iran says it has spent more than $700 million on building a "wall" along lengthy stretches of its 1,700-kilometre (1,050-mile) eastern border with Afghanistan and Pakistan in a bid to stop the trafficking.
Tehran's anti-drugs efforts are regularly praised by the United Nations Office on Drugs and Crime, which provides the country with financial and other assistance.
However, the United States has accused some Iranian officials, particularly within the elite Revolutionary Guards, of facilitating the transit of drugs produced in Afghanistan in exchange for services of drug lords.
Iranian officials in return accuse Western and Israeli intelligence services of promoting drugs in the Islamic republic in an effort to destabilise the country.