Before an international meeting in Vienna on March 13-14 on global efforts to combat narcotics, Fedotov said that Iran takes a very active role to fight against illicit drugs," he told reporters.
In 2012, Iran seized 388 tons of opium, the equivalent of 72 percent of all such seizures around the world.
"It is very impressive," Fedotov said.
Fedotov made clear the UNODC was not considering halting support for Iran due to death penalties in the Islamic Republic, Al-Manar reported.
"I don't believe that the international community would welcome this because it would mean, as a possible reaction from Iran, that all these huge quantities of drugs, which are now being seized by Iranians, would flow freely to Europe," he said.
Iran shares a long border with Afghanistan, which supplies about 90 percent of the world's opium, from which heroin is made. Iran says it has lost many security personnel in skirmishes with drug traffickers in volatile regions bordering also Pakistan.