NATO has imposed tough new restrictions on foreign journalists covering the war in southern Afghanistan, changes that could affect how much Canadians see and hear from war-torn Kandahar.

The new measures, imposed in early March, mirror the way the U.S. military manages reporters in Iraq.

The restrictions make it virtually impossible for Canadian journalists to leave Kandahar Airfield on their own to interview local Afghans and return unimpeded to the safety of NATO's principal base.

Last month, Canadian soldiers were required to escort newly arrived journalists everywhere on the airfield, including to the dining hall and showers. A photographer from the Reuters news agency and a handful of Canadian journalists were escorted between buildings and confined to their sleeping quarters when not working.

The practice has been temporarily suspended under pressure from the Canadian military, which has tried unsuccessfully to have the overall policy reversed.

Some of the new rules do not apply to American journalists because the measures would violate their rights under the U.S. constitution.

A Canadian defence critic and an organization that represents journalists condemned the new rules, accusing the U.S. of trying to shut down Canadian coverage.

"The media is not the enemy and this is a form of censorship — and it is unacceptable," Liberal MP Denis Coderre said Tuesday. "There is a public interest to know what's going on in the field."

The new rules came as Washington prepared to deliver an additional 21,000 combat soldiers and trainers to the country to confront the revived Taliban insurgency.

Security officials at Kandahar Airfield, including the base commander, declined to comment on the measures. Officials at the Canadian Expeditionary Force Command in Ottawa would not comment on the record, but suggested NATO headquarters in Kabul was looking at the matter.

Mary Agnes Welch, president of the Canadian Association of Journalists, called on the Harper government to put pressure on the Pentagon to reverse the policy.

"You can make the argument that this is exactly one of the reasons that we're in Afghanistan — that the press have free and unfettered access to as much of the story as they can reasonably get to," she said from Winnipeg.

The Canadian military has presented NATO's southern commander with proposals to end the dispute, but none has been accepted.

Welch said the "radical shift" in policy takes away the Canadian media's ability to cover the conflict independently.

"It sounds like the more control they have over journalists, where they go, who they talk to, they'll be able to shape the story in a much effective way," she said.

"That ultimately is not effective for Canadians' understanding of what's really going on."

The new U.S. security team at Kandahar Airfield stopped issuing International Security Assistance Force accreditation to journalists in late February. Instead it gives them temporary base visitor passes, which restrict movements and require them to be closely monitored.

The reporters are also compelled to forfeit their passports to the military for the duration of their stay.

Canadian news organizations, which use the airfield as a base to cover the country's 2,850 troops and aircrew, are the most affected. Other NATO countries have sent small teams of reporters through Kandahar on a short-term basis.

Journalists routinely leave the airfield to pursue the Afghan side of the story, chronicling among other things allegations of torture among Taliban prisoners and the plight of refugees bombed out of their homes.

Early in the winter, NATO officials in Kandahar began demanding that Canadian journalists be given a full federal government security screening, involving background checks, before they would issue accreditation. It was a step up from the previous criminal-record check. Informally reporters were told the request was made because some U.S. private contractors had been accused of theft.