US Ambassador to Afghanistan Ronald Neumann speaks to media during a press conference at his embassy in Kabul

U.S. officials in Afghanistan say the country's powerful drug cartels are fueling the region's violent insurgency, in order to protect their own illegal opium networks. The allegations come amid a sharp rise in insurgent attacks in recent weeks.

U.S. Ambassador Ronald Neumann told reporters that drug lords, mostly in Southern Afghanistan, hope the insurgency will effectively incapacitate Afghan President Hamid Karzai's counter-narcotics program.

"This year, President Karzai led a very strong policy to eradicate poppy. There were efforts by drug-dealers and terrorists together to prevent that," he said. "They did not prevent it, and, I think, now, they are trying to use the violence to guard their wealth."

The U.N. says roughly two-thirds of the world's opium supply is cultivated in Afghanistan.

The illegal harvest produces billions-of-dollars every year, most of which is controlled by a relatively small group of powerful drug barons.

The largest harvests are found in Southern Afghanistan in Helmand and Kandahar provinces, which are also the Taleban's traditional strongholds.

Violence throughout the region has surged in recent weeks, as Taleban militants stage a series of deadly anti-government attacks.

The insurgent offensive comes as NATO gets ready to take over security operations in Southern Afghanistan.

By the end of July, U.S. forces in the region will be replaced by NATO peacekeepers, primarily British, Dutch and Canadian troops.

Ambassador Neumann says the Taleban are apparently trying to intimidate the less experienced NATO troops, who are arriving in Afghanistan.

"This is being proved wrong, and I think that a lot of people who believe the Taleban fight with them are going to die, because these forces will fight very strongly," noted Neumann.

U.S. and NATO forces say they have already responded to the Taleban attacks with their own string of powerful counter-strikes.

In the past month, more than 500 people have been killed, most of them militants.

Afghan officials say local and U.S.-led coalition forces in Southern Afghanistan killed another 37 suspected insurgents, including a brother-in-law of the Taleban's fugitive leader Mullah Mohammad Omar.