KARACHI, Pakistan (AP) _ Pakistani authorities say they have arrested seven people who allegedly smuggled tons of heroin to Europe through the mail.

The gang had smuggled about 3 tons of heroin worth billions of dollars during last 13 years, with each envelope containing up to 10 grams of heroin powder.

``It was a major international gang,'' Mukhtar Ahmed, director general of Anti-Narcotics Task Force, told reporters Tuesday.

The arrests came this week after several months of investigations, but the gang leader escaped, he said.

Poppy is cultivated in Pakistan's northern areas bordering Afghanistan. Most heroin manufacturing factories also operate in the border areas of the two countries.

Pakistan launched a massive crackdown on poppy fields recently, but has been unable to destroy them completely because of resistance from locals.