Madrid - The Spanish government on Monday called for calm after Europe's first case of swine flu was confirmed among a total of at least 21 cases suspected in the country.

None of the patients were in a serious condition, Health Minister Trinidad Jimenez said, explaining that Spain had the means to face a possible epidemic.

The minister admitted, however, that the health authorities were "worried" and "on the alert."

A 23-year-old man was diagnosed with swine flu on Monday after returning from a study trip to Mexico on April 22.

The patient was being kept in isolation at a hospital in Almansa in the south-east of the country.

At least 20 other suspected cases were also kept isolated around the country. They were mostly young people who had returned recently from Mexico. The authorities were identifying passengers who had been on the same flights.

The diagnosed patient and the others were in a stable condition, and responding well to treatment, Jimenez said, describing the situation as being "under control."

Health measures were being stepped up at airports, and airlines would be asked to inform passengers about the risk of swine flu especially on flights to Mexico and the United States, where cases have been detected, she explained.

Spain still had 10 million doses of the Tamiflu vaccine, which it acquired earlier to face an eventual bird flu pandemic, and which could be of use against swine flu as well, Jimenez said.

Swine flu was transmitted only between humans or from pigs to people who were in direct contact with the animals, for which reason it was safe to eat pork and related products, the ministry said on itsb website.

Jimenez said no pigs on Spanish farms suffered from the disease.

The shares of tourism-related companies such as airlines and hotels fell on the Madrid stock exchange following the news.

Jimenez advised Spaniards not to travel to Mexico if they could avoid it, and to monitor their health for 10 days if they had just returned from the Latin American country. The Foreign Ministry issued a similar advisory.

The number of dead in Mexico's potentially deadly flu outbreak rose to 103, with at least 20 cases confirmed as swine flu, according to authorities.