NATO's top commander said Friday the alliance likely will expand its Afghan mission by year's end to include the entire country, including the lawless east where militants killed a coalition soldier in the latest fighting.

The Dutch military said its commandos killed 18 militants in an operation to clear rugged hills near a base for its forces deploying in the insurgency-wracked south, where NATO is preparing to take over the security command by the end of this month.

In recent months the region has witnessed some of the worst fighting since the Taliban was ousted in late 2001. The militants have stepped up suicide attacks and assaults on Afghan and U.S.-led coalition forces. More than 800 people, mostly militants, have died in violence nationwide since mid-May.

NATO's supreme commander, U.S. Gen. James L. Jones, said member nations were expected to approve a plan to expand across Afghanistan at the alliance's November summit in Latvia.

"Certainly by the Riga summit or sooner we should be able to achieve this," Jones told reporters in the southern city of Kandahar.

NATO forces already have a presence in the capital, Kabul, and the western and northern regions.

Two senior British army commanders said that Taliban guerrillas posed a severe threat to NATO troops but would be beaten, despite significant shortfalls in logistical support.

Lt. Gen. David Richards, the commander of NATO's International Security Assistance Force in Afghanistan, told a London think tank that the force lacked sufficient helicopters and reserve troops for rapid deployment.

Richards said the financing and logistical backup for the mission might not "keep up" with the requirements of NATO operations in Afghanistan.

"This will, undoubtedly, jeopardize success," he said. "We are not unable to operate, but we could do it more efficiently," he said.

Brigadier Ed Butler, the commander of Britain's 5,000-strong contribution of troops to the NATO mission, said the level of Taliban resistance to NATO forces had surprised him.

"We knew it was going to be tough, and we knew that the Taliban would test our resilience and, possibly, in some cases we have been a little surprised by the ferocity and persistence of the Taliban," Butler said during a visit to an army base east of London. "But hopefully it will not be too long before the tide does turn."

A NATO delegation reviewing the alliance's expansion into southern provinces toured the region Friday, visiting British, Dutch and Canadian soldiers building camps in blistering heat.

A coalition soldier was killed by militants Thursday in Sharan, the capital of southeastern Paktika province, when they hit a coalition compound with rockets and mortars, the coalition said. The soldier's nationality was not released.

NATO Secretary-General Jaap de Hoop Scheffer, who joined Jones in the delegation, acknowledged the difficulty of the alliance's mission in the south — to defeat the Taliban and promote reconstruction — but said it could not be allowed to fail.

"I think everybody realizes that this is not only NATO's largest mission but the most important, so it has risks," de Hoop Scheffer said in Kandahar.

NATO-led troops deploying to the south — mostly British, Canadian and Dutch forces — currently work with U.S. troops as part of a campaign against the resurgent Taliban.

NATO's troop strength nationwide should reach about 18,000 by September.

The United States has at least 21,000 troops in Afghanistan, many of which will be incorporated into the NATO force. However, the United States will maintain a combat force independent of NATO to hunt down Taliban and Al Qaeda militants.