U.S. Defence Secretary Donald Rumsfeld vowed that the Taliban will be defeated on a surprise visit to Afghanistan on Tuesday, denying charges that coalition forces are losing the battle against insurgents.

At a joint news conference with Afghan President Hamid Karzai, Rumsfeld asserted in Kabul that militants "don't want to see a country like Afghanistan have a successful democracy. They won't succeed."

Rumsfeld, who arrived unannounced on his 11th trip to Afghanistan, said that while the war-torn country's neighbours were helping to prevent militants from entering the country, they needed to do more.

Rumsfeld is in Afghanistan to discuss plans for NATO to take over military operations from a U.S.-led force in the south this month.

The defence secretary also called on Europe to provide a "master plan" to Afghanistan to help curb its massive drug trade, which has seen heroin flood Europe and Russia.

Rumsfeld said the drug's spread was of concern not just for Afghanistan but for Europe where opium is in wide use.

"It seems to me that it is important for them (Europe) to recognize that it is a lot cheaper ... for them to assist the Afghan government in providing master over-all plan for dealing with the counter-narcotic effort," Rumsfeld.

Though the international community funnels hundreds of millions of dollars into anti-drug campaigns, Afghanistan still produces more than 90 per cent of the world's opium and heroin supply.

The illicit trade is particularly prolific in southern Taliban breeding grounds, where the militant group is believed to benefit from income generated from the drug's production.

Speaking after the talks with Rumsfeld, Karzai praised the United States for the help it provided to Afghanistan.

"Without the United States, Afghanistan would have not been a free country today," he said. "Without the United States, Afghanistan would have, even now, been ruled by al Qaeda and terrorism."

Karzai's remarks came hours after the top U.S. commander in Afghanistan said the rise of Taliban resistance in the south reflects the weakness of the government rather than the strength of the fundamentalist movement.

"The areas that the Taliban is operating in are areas that the government of Afghanistan has not heretofore had the strength and had the presence," Lt. Gen. Karl Eikenberry told reporters before boarding a plane in Dushanbe, Tajikistan with Rumsfeld.

Eikenberry said the insurgents are operating in areas where the government has little presence.

"It's not a question of the enemy being strong," he added. "It's very much a question in many instances of the institutions of the state of Afghanistan still moving slowly to stand up in governance and Afghan national security forces. But we very much have the momentum."

Eikenberry said the Taliban has been able to assert itself, particularly in the south. "The Taliban is more organized than they were last year and they have more fighters in certain areas," he said.

Britain announced on Monday it would send 900 more troops and additional helicopters to Helmand where troops have faced fierce Taliban resistance.

The reinforcements will arrive over coming months bringing the total to 4,500 in the south.

In the latest fighting on Tuesday, coalition forces and Afghan troops killed about 30 militants in the southern province of Helmand.

The raid was conducted as part of Operation Mountain Thrust, a campaign involving more than 10,000 coalition and Afghan troops.

Coalition and Afghan troops suffered no casualties in the operation in the Sangin district, military officials said.