Russia and Slovakia tightened their borders with Ukraine on Tuesday as the World Health Organization began investigating a suspected swine flu outbreak.

The death toll from flu has climbed to 71 since the outbreak struck last week in the western city of Ternopil, Prime Minister Yulia Tymoshenko said.

Blood tests have yet to determine how many of these deaths were from the new and aggressive H1N1 strain. But the WHO said in a statement on Tuesday that most flu cases in Ukraine can be assumed to be H1N1, "as the pandemic virus has rapidly become the dominant influenza strain worldwide."

As a precaution, schools and universities across the country will remain closed this week, and officials urged people in western Ukraine to travel only when necessary and stay away from public places.

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Slovakia, which lies on Ukraine's western border, closed two of its five border crossings with Ukraine to keep the infection from spreading. In Russia, where there have been 14 confirmed swine flu deaths, the Health Ministry said it would examine anyone crossing the border from Ukraine and quarantine people with severe symptoms.

The World Health Organization sent a team to Kiev on Monday to assist local health officials with the epidemic. It recommended against restricting travel or closing borders, calling such measures ineffective in preventing the spread of the virus.

The Ukrainian government's precautions have been reasonable considering the potential threat, WHO spokesman Gregory Hartl said.

"By closing schools and canceling mass gatherings in the early stages of an event ... you can slow down the transmission of the virus," Hartl said by phone from the organization's headquarters in Geneva. "So far there is only one confirmed death (from H1N1 in Ukraine), but there is a big event going on there."

The WHO is focusing its efforts on the western city of Lviv, "where reported numbers of cases showing severe manifestations of acute respiratory illness have been especially high," it said.

The government has already urged cafes, cinemas and theaters to close indefinitely in Lviv, and roughly a third of the people in the streets on Tuesday wore surgical masks to avoid inhaling the virus, as did the Ukrainian guards on the border with Belarus.

But the emergency ward of the central hospital in Lviv saw no shortage of available beds, even as patients trickled in complaining of flu symptoms on Tuesday. All of those accepted for treatment were quarantined.

Compared to last year, the total number of flu deaths in Ukraine has actually dropped by 10 percent, the UNIAN news agency quoted Deputy Health Minister Vasily Lazorishinets as saying.

This led some Ukrainian officials and medical experts to accuse the government of exaggerating the outbreak for political gain ahead of presidential elections to be held in January.

In January, Tymoshenko and President Viktor Yushchenko will face off for the presidency. That election could overturn the 2004 Orange Revolution that swept a pro-Western government to power in Ukraine for the first time. Leading in the polls is Viktor Yanukovich, who was beaten in 2005 by Yushchenko, but has pulled ahead on a platform that emphasizes closer ties with Russia.