High-potency heroin from Afghanistan is causing a surge in deadly drug overdoses in Los Angeles County, officials said, according to a report in the Los Angeles Times.

"The rise of heroin from Afghanistan is our biggest rising threat in the fight against narcotics," Orange County sheriff's spokesman Jim Amormino told the newspaper. "We are seeing more seizures and more overdoses."

According to the report, heroin-related deaths in the county have soared 75 percent in three years, from 137 in 2002 to 239 in 2005.

The Times cited a Drug Enforcement Administration report it obtained as saying that the poppy fields in Afghanistan have become the fastest-growing source of heroin in the U.S.

The heroin from Afghanistan is the purest in the world, according to the DEA's National Drug Intelligence Center.

According to the DEA report, Afghan heroin dominated the U.S. market from 1980 through 1985, with a 47% to 54% share, but that dropped to 6% for much of the 1990s, as the Taliban cracked down on poppy production.

Since the overthrow of the Taliban government in 2001, Afghans have returned to growing poppies.

According to the DEA report, opium production accounted for more than one-third of Afghanistan's gross domestic product and 90% of the world's supply of illicit opium, the Times reported.