ZARANJ, Afghanistan — Seen from the air, the Margo desert, which sprawls across the far southwestern corner of Afghanistan toward the borders with Iran and Pakistan, is traced with white car tracks.

With its forbidding reputation as the "desert of death," it deters most travelers but is the favored route of drug traffickers taking opium, heroin and hashish produced in Afghanistan to Iran for smuggling to Turkey and Europe. They cross in armed convoys of 10 to 20 pickup trucks, at such high speed that police officials say they cannot catch them.

"The smugglers know the desert very well," said the police chief of Nimruz Province, who goes by one name, Asadullah. "They have very powerful cars, Landcruisers that go at 250 kilometers an hour [155 mph]."

The desert crossing is part of a lucrative drug trade that threatens to turn Afghanistan into a narco-mafia state, U.N. officials say, adding that Afghanistan, the biggest producer of opium in the world, is the source of 90 percent of the heroin on Europe's streets.

There are three main routes for drugs out of Afghanistan: from the northeast into Tajikistan and on to Russia; into Pakistan and its ports; and westward across the desert into Iran.

Of the three, this corner of Afghanistan, where Baluch tribesmen have survived by banditry and smuggling for centuries and tend not to recognize national boundaries, is perhaps the most notorious.

The profits from trafficking are easy to see here in this dust-blown, arid town on the border with Iran. Farmers have been ruined by a seven-year drought, and townspeople have to fetch their drinking water in plastic containers from public taps. But lavish villas, decorated with colored tiles and mirrored glass, are being built.

"That house belongs to a drug smuggler," said Ghulam Ghous Sistani, the chief of the counternarcotics team in Nimruz, pointing to a new white villa as he drove through the town. He showed half a dozen more, naming the owners each time. One also owned a hotel in the capital, Kabul, he said.

The fancy houses have gone up just in the last year, indicating a confidence among drug smugglers that they can buy land and build freely in Afghanistan these days.

Catching even the couriers is extremely difficult, Sistani said: "They go straight through the desert to the border. They have rocket launchers and machine guns. We don't have the power to fight them."

Just 10 days earlier, Sistani was on patrol in the desert when he spotted a drug convoy. "I was in my own car," he said. "They were in six cars, with about 15 to 20 armed men. They saw us but they were not scared of us."

"We have no vehicles, no radios. No one helps us. ... We should have 15 fast cars, weapons, satellite telephones, otherwise we cannot fight them.

"When I get invited to meetings in Kabul, they always say Nimruz is the place of smuggling, and I say: 'How can we stop it?' "

The Iranian authorities and the United Nations have confirmed the scale of the problem and the deadly seriousness of the smugglers. Iran has lost more than 3,000 police officers battling the drug smugglers in the past 10 years, Muhammad Bahrami, Iran's ambassador to Afghanistan, said in a recent interview.

The Afghan police said tough paramilitary policing by Iran had forced the smugglers to reduce the scale of the convoys and even to revert to camel trains. But on this side of the border, Sistani said, Afghans are catching people only at the lower end of the smuggling operation.

Inside a metal shipping container at the police station, he showed off more than 1,200 pounds of confiscated heroin, opium and hashish, as well as a small stove used for processing morphine.

"We caught these on donkeys, camels and motorbikes," he said. "The rule is the same the world over; they dump the drugs and run away."