KANDAHAR, Afghanistan — The top diplomats from Britain and America made an unannounced visit to one of Afghanistan’s most dangerous corners yesterday in a show of support for North American Treaty Organization allies that have been willing to suffer casualties in the fight.

Secretary of State Rice and British Foreign Secretary David Miliband flew to this southern city, the cradle and former headquarters of the militant Taliban movement, to salute 200 NATO troops at the sprawling Kandahar Air Base.

“On behalf of the people of the United States, thank you, thank you, thank you,” Ms. Rice told the troops, who were primarily Canadian, Dutch, British, and Australian.

Although she denied any intention to slight other countries, her words carried a bite because NATO is locked in an intensifying internal struggle between member nations that have been willing to send combat troops to the most dangerous parts of Afghanistan and those that have limited assignments to safer zones.

Ms. Rice spoke to the forces in the southern town just weeks after Defense Secretary Robert Gates criticized NATO troops there as lacking adequate training in counterinsurgency techniques, touching off a political firestorm.

Ms. Rice made it clear, as Mr. Gates has, that she intended to continue pressing the Western allies to step up their contributions. “It’s not an overwhelming number of forces that is being sought here,” Ms. Rice said. “This is a troop contribution level that NATO can meet and should meet.”

“As the debate heats up about what you are doing here, we will be defending you heart and soul,” Mr. Miliband told the group, which had gathered amid low-slung beige buildings and barbed-wire-festooned walls.