PARIS - Governments and tour firms on Wednesday tightened a virtual travel quarantine imposed on Mexico over deadly swine flu even though many experts doubt the impact of restrictions.

Cuba and Argentina suspended flights to and from Mexico for 48 hours late Tuesday in the toughest reactions yet to the flu which has been blamed for more than 150 deaths in Mexico.

The Cuban move was ordered for 48 hours while Argentina halted flights to and from Mexico until Monday.

Cuba has not yet seen a single suspected case of swine flu, said Deputy Health Minister Luis Estruch Rancano. "The danger does exist, but the country is already taking appropriate measures," he said.

Tour companies from several countries have stopped holiday operations and many governments have issued warnings against travelling to Mexico as the World Health Organisation (WHO) steps up pandemic warnings.

The United States, Japan, Britain, France, Israel, Canada, Argentina, Switzerland, Vietnam, Australia and a host of other countries have issued warnings against travelling to Mexico. Iran has told its people not to go to Mexico or the United States, where more than 60 swine flu cases have been confirmed.

Most of the cases of swine flu outside of Mexico are people who have just visited the country and tour companies have been forced act over the growing alarm.

Canadian airline Air Transat said it was suspending flights to Mexico until June 1 after the WHO raised its flu alarm to level four "and following directives issued by governments because of the appearance of swine flu in several countries."

The two main French associations for travel companies halted all departures for Mexico on Tuesday. Major tour operators across Europe, including Thomas Cook and TUI, have halted flights to Mexico over the swine flu outbreak.

Thomson travel and its sister company First Choice suspended flights to Mexico and said they would begin repatriating thousands of people already there.

Major cruise companies such as Royal Caribbean, Carnival and the Norwegian Cruise Line -- who every day transport thousands of holiday makers around the Caribbean -- announced they have halted visits to Mexican ports.

The WHO has so far not recommended travel restrictions because of swine flu, but the European Union's main disease prevention agency has urged a travel ban.

"What we are recommending is that EU citizens should only travel to Mexico if it is unavoidable and absolutely necessary," said Zsuzsanna Jakab, the director of the European Centre for Disease Control.

The ECDC position differs from EU Health Commissioner Androulla Vassiliou, who said Tuesday there was no need for travel restrictions.

"Precautionary measures are advisable but at this juncture I don't see any point on restricting travelling," she said.

Angus Nicoll, head of the ECDC's influenza programme, acknowledged that travel bans make "very little difference" in stopping the spread of the virus.

"The difficulty at the moment is that you have one country where people have died, people have got very sick, some European citizens who have gone there have been infected," Nicoll said.

"It is quite difficult to say to a family going on holiday to Mexico: don't worry, off you go," he added.