In the absence of answers, American and NATO officials agreed to form a joint commission with the Afghan government to investigate. Still, a senior NATO spokesman, Brig. Gen. Günter Katz of Germany, said at a news conference on Monday that a previous inquiry could not confirm abuses by Western forces or Afghans working with them in Maidan Wardak. “So far, we could not find evidence that would support these allegations,” General Katz said. The ban did, however, drastically reinforce that Mr. Karzai has become the dominant voice in establishing how the final stages of the Western military involvement in his country will be conducted. And in the past year, he has appeared increasingly willing to curtail unilaterally the coalition’s role on issues of most concern to him: special operations missions, detentions and airstrikes.

As they have in past points of tension with Mr. Karzai, American officials maintained a conciliatory tone in their public comments on Monday.

Speaking to reporters in London, Secretary of State John Kerry said that Mr. Karzai “had many legitimate evaluations of how sometimes some things have gone or might be changed and be done better.”

Mr. Kerry cited talks on a security agreement that would keep American forces in Afghanistan after the NATO combat mission ends in 2014, and efforts to jointly manage the transition process away from coalition leadership now under way. “We’ve listened very carefully to his observations about wanting to speed up the transition with respect to the management of security,” he said, “and that’s happening.”

If anything, Mr. Karzai has set the pace of transition over the past year. He has repeatedly demanded and won greater Afghan control of the war effort, occasionally taking his confrontations with American officials public.