South Korean police said Friday they have arrested members of a major drug-trafficking ring with suspected links to Afghanistan's Taliban insurgents.

"Police have rounded up a drug-trafficking ring involving Afghans and Pakistanis who are suspected of being linked with the Taliban," a National Police Agency spokesman told AFP.

"They are suspected to trying to smuggle raw materials for heroin production into Afghanistan," he said.

Police said two Afghans, three Pakistanis and four Koreans tried to use South Korea as a shipping point for several tons of acetic anhydride destined for southern Afghanistan.

The chemical is heated with morphine, extracted from opium, to produce heroin.

"The key Afghan suspect admitted he did it at the instigation of the Taliban," Oh Ki-Duk, an investigator, told AFP. "But he claimed he is not a member of the Taliban."

Police confiscated 12 tons of acetic anhydride in a chemical engineering factory in the Seoul suburb of Ansan and arrested the two Afghans. The chemical was disguised as motor oil.

In a separate operation by the three Pakistanis -- who were also arrested in a Seoul suburb -- police said about 50 tons of the chemical had already been shipped, labelled as disinfectant.

It was sent between April 2007 and March this year.

The operations were funded by the hawala money transfer network widely used in the Middle East, police said.

The 62 tons of acetic anhydride cost about 360 million won (344,800 dollars) but could be used to produce nearly 30 tons of heroin, Yonhap news agency quoted investigator Kim Ki-Yong as saying.

"The suspects had money transferred from accounts suspected to be linked to hawala, and they acknowledged they had received orders from the Taliban," Kim said.

The acetic anhydride was imported from Japan through several Korean dealers, who are now being questioned.

The investigation started in March after the international police organisation Interpol discovered 14 tons of the chemical which had been shipped from Korea in the southern Pakistani port of Karachi.

The United Nations Office on Drugs and Crime says Afghanistan produced 8,200 tons of opium base last year, 92 percent of the worldwide total.

The report also noted that 80 percent of the output came from five southern provinces where Taliban insurgents profit from drug-trafficking.

Last year 23 South Korean missionaries were captured and held hostage in Afghanistan by members of the Taliban.

Two of them were murdered before the South Korean government reached an undisclosed deal to free the remainder.