The risks of a potential pandemic outbreak of the deadly swine flu are rather high, Russian scientist Dmitry Lvov warned on Tuesday, saying countries around the world must take urgent measures to prevent panic.

Lvov, director of the Virology Research Institute at the Russian Academy of Medical Sciences, said that swine flu could reach Russia "within hours, or days maximum, anyway within a week," as quoted by the RIA Novosti news agency.

It is almost impossible to prevent the virus from entering Russia, said Lvov.

Russia has taken special control over passengers from North America, as those running a fever would be quarantined until the cause is determined.

"A vaccine against swine flu could be developed at best in six months," he added. The World Health Organization (WHO) set a similar time period between four to six months.

According to Lvov, "the virus is a cross-breed of the American and European swine flu viruses."

"At this point it remains unclear why the virus is so virulent, or what sort of mortality rate it may cause. It is very important to remember that it is well transmitted from human to human," the Itar-Tass news agency quoted him as saying.

As for precautious measures, Lvov advised people to receive commercial vaccines containing H1N1 components, and to avoid crowded places while spending more times outdoors breathing fresh air.

Meanwhile, Lvov said that: "the risk of being infected with meat is equal to zero."

Russia on Sunday banned meat and meat product imports from Mexico and three US states, as well as pork and pork products from several Latin American countries and US states.

However, another Russian expert, Ilya Drozdov, believed that the lethal virus currently poses no threat to Russia.

The director of the State Scientific Virology and Biotechnology Center said on Tuesday that "We do not regard the situation as dangerous in the foreseeable future," according to RIA Novosti.

The WHO on Monday raised its pandemic alert level from Phase 3 to Phase 4, which means the swine flu virus can cause sustained human-to-human transmission and "community-level outbreaks."

The flu has killed 152 people in Mexico and has spread to other countries. There are 51 confirmed cases in the United States and six cases in Canada.

None of the other cases reported in countries including the United States, Canada, Spain, Scotland and New Zealand have proved fatal to date.