The South Korean military said on Tuesday that it raised the alert against swine flu as the country's health authorities reported the first suspected case early Tuesday morning.

"The military authorities have ordered that any soldier suspected of showing flu symptoms be reported to them immediately," Won Tae-jae, spokesman for the Ministry of National Defense, said.

"The ministry has also ordered officers to refrain from overseas traveling," he said, adding that there hasn't been any case of contraction in military yet.

Health officials said earlier in the day that a 51-year old woman from a recent trip to Mexico was suspected of human infection of swine influenza for the first time in South Korea.

About 150 people are believed to have been killed in Mexico by the swine influenza virus, which is transmittable among humans.

The United States, Canada and some European countries have also reported human cases of the flu, which drove the World Health Organization (WHO) to heighten its alert level to the third highest.