A special committee appointed by Mr. Karzai to investigate the companies has found that 18 have committed “major offenses,” although that number may have later been lowered, according to an Afghan official who has read the committee’s report.

While the offenses cited were less than explosive — there were no charges, for instance, of murder or the inadvertent killing of innocents — some Western officials worry that Mr. Karzai may use them to try to speed the departure of the companies faster than his government is able to replace them with a promised Afghan force.

“If push comes to shove, it could be a very big deal if they went through with the proposal to rid the country of all private security companies,” one Western diplomat said. “But we’re not sure where we are yet in terms of which companies will be allowed to stay and which will be asked to leave.”

At the same time, the government has ordered financial audits on 33 of the 55 private security companies operating in Afghanistan, officials said. This examination, which focuses mainly on whether some companies failed to pay taxes, constitutes a separate track the government could use to put pressure on them.

Mr. Karzai issued a decree in August banning most private security companies in an effort to bring under government control the thousands of private guards who have often been accused of corruption, reckless use of force and in some cases acting as de facto militias.

But NATO, foreign embassies and aid groups that depend on private companies to provide security protested the rule, and companies involved in development projects said they would have to cease their work if they could not protect their employees.

In December, the government backed off, agreeing that private security companies would be gradually phased out as government guards were recruited and trained to take their place.

The special committee’s report, issued this month, has revived international concerns.

The committee, created in November, includes representatives from the Afghan National Security Council and the Interior, Finance and Foreign Affairs Ministries, among others.

The 18 companies cited for “major offenses” were not identified by the official who provided information about the committee’s report on condition of anonymity.

The accusations against them include the illegal use of weapons, illegal hiring, vehicle offenses and tax evasion, according to the official. Seven other companies were also found to have links to high-ranking Afghan officials and politicians.

While the offenses may not seem heinous for a war zone, the failure to register weapons or the names of employees is a serious issue for a government concerned about the spread of private militias, the proliferation of weapons and shifting loyalties among government forces and those of insurgents and warlords.

Gen. Abdul Ghafar Saidzada, chief of counterterrorism for the Interior Ministry, who was involved in the creation of the report, said that it was still a work in progress and that Mr. Karzai had not yet made any decisions based on it.

A separate list of offending companies compiled by the Interior Ministry has been circulating among Western officials. This list contains 16 companies under the category of “major offenses.” Nine are cited for “medium” offenses and 11 for “minor” ones. Details of the offenses were not specified. The existence of this separate list was reported Sunday by The Washington Post.

This list, obtained by The New York Times, cites nearly two-thirds of the private security companies operating in Afghanistan as having committed some offense.

It appears that the list emanated from the special committee’s investigation, though it was not immediately clear why there was a discrepancy in the number of companies cited for different offenses. Some offenses initially listed as major may have been downgraded to lesser categories, one official suggested.

How the list was compiled has also caused concern.

Alissa J. Rubin and Ruhullah Khapalwak contributed reporting.