Members of France's elite intervention squad are already riding undercover on some trans-Atlantic flights, while a continent away, Mexican security agents also began boarding planes before a new U.S. directive to foil foreign terrorists.

Many airlines around the world have said they would cooperate with the U.S. order announced Monday to put armed law enforcement officers on certain international flights as part of a heightened terror alert. Some others say they have used armed marshals since shortly after the Sept. 11, 2001, terror attacks.

With fears of terror rising this holiday season, France (search) and Mexico (search) were among nations quick to bolster security.

There are doubters.

The International Air Transport Association (search), an industry group of 275 international air companies, joined a chorus of professionals who would prefer more prevention on the ground rather than a potential shoot-up in a high-flying aircraft.

New Zealand's Civil Aviation Authority said Wednesday that armed marshals will not be aboard New Zealand flights to the United States "any time soon."

"In the highly unlikely event that it [the U.S. directive] applied to New Zealand then it would have to be considered by government," aviation authority spokesman Bill Sommer told reporters.

Thailand's Prime Minister Thaksin Shinawatra said there was no need for armed guards on Thai Airways flights to prevent terrorist attacks. "We have a system of checking at the departure point already," he told reporters.

Finland's national carrier Finnair said flatly that it would rather ground its aircraft than put armed marshals on board.

Homeland Security Secretary Tom Ridge on Tuesday hailed the response of other nations. "I'd put the family on the plane," Ridge said when asked about how strongly he felt about new safety measures the Bush administration has undertaken.

Under Ridge's new directive, the government would have the option of denying access to U.S. airspace to airlines unless they put an armed officer on flights crossing over or headed to the United States.

Mexico said Tuesday it reached an early agreement with Washington and has had security agents on board some flights since last week. The agents carry weapons with special ammunition designed to avoid loss of pressure in the aircraft cabin if fired, said Public Safety Secretary Alejandro Gertz.

France, always keen to dictate its own policy, has made no official announcement about compliance with the U.S. directive. However, special teams have been aboard some Air France flights reportedly for the past week.

Interior Minister Nicolas Sarkozy, speaking during a visit to Cairo, confirmed that France has stepped up security, but refused to reveal "either the modalities or the timing of this strategy of reinforcement."

"What is clear ... is that the threat is so large and diffuse that we cannot compromise," said Foreign Ministry spokesman Herve Ladsous. "So the obligation to cooperate is absolutely clear in the eyes of all countries concerned by this threat."

According to an official close to the situation, teams from an air security unit are aboard some Air France flights to the United States.

They are armed with specially adapted weapons "so as not to put lives in peril ... or the integrity of the aircraft," the official said, speaking on condition of anonymity.

The newspaper Liberation reported Tuesday that two to six members of the National Gendarmerie Intervention Group have been traveling on certain flights since Dec. 23, armed with electrical stun guns.

A French delegation that included intelligence agents met on Monday in Washington with Ridge and CIA and FBI officials to discuss counter-terrorism and international flight security.

Cooperation with the United States is "exemplary," but matters like the extent of the U.S. program and risk evaluation remained under discussion with Washington, the Foreign Ministry spokesman said.

Air France canceled six flights between Paris and Los Angeles over Christmas, after security discussions between U.S. and French officials. France's flag carrier has said only that unarmed security agents had been aboard "flights judged to be sensitive" since the Sept. 11, 2001, terror attacks on New York and Washington.

Germany's Lufthansa and Transport Canada are among airlines that say they have carried sky marshals on some flights since shortly after the 2001 attacks by the Al Qaeda network.

Air Canada said it was complying with the U.S. request for armed officers on board certain flights.

Russia's aviation authorities said there had been no government decision on whether to comply with Washington's demand.

The Swedish aviation authority wants to avoid weapons onboard flights if possible, said Eva Axne.

Britain has said it would deploy sky marshals "where appropriate," but pilots have expressed strong reservations about the plan.

Britain's airline pilots' association called Tuesday for an emergency world summit of airline pilots to consider the U.S. demand for sky marshals.

"Our advice to pilots is that until adequate written and agreed assurances are received, flight crew should not operate flights where sky marshals are carried," said the group's chairman, Mervyn Grandshaw.

Many of those opposed to the U.S. directive want the emphasis placed on nabbing terrorists on the ground.

IATA said that "aside from specific, identified threats, the international airline industry continues to believe that security resources are best allocated to ensure that threats do not get on board the aircraft."

Eric Lahon, of France's Alter pilot union, said armed marshals aboard a plane amount to an admission of lapsed security.

"To imagine that we're going to solve a terrorism problem by putting cowboys on board planes is to admit that we failed at all security measures on the ground," he said.