MOSCOW, July 28 (RIA Novosti) - The number of Russians who have contracted the A/H1N1 virus has risen to 28, Russia's sanitary watchdog said on Tuesday.

Swine flu cases have been registered not only in Moscow and central Russia, but also in the Volga Region, the Urals and Siberia.

All the people diagnosed with swine flu in Russia had recently returned from vacations or business trips abroad, mainly from Britain and Spain.

The World Health Organization (WHO) has confirmed 160,038 officially registered swine flu cases including 991 deaths in 135 countries and territories worldwide.

Russia's top sanitary official, Gennady Onishchenko, announced on Tuesday a temporary ban on the travel of groups of Russian schoolchildren to Britain for language courses.

"I signed a directive...to stop the travel of children groups to Great Britain in August," Onishchenko said on Mayak radio.

"Everybody knows that the number of swine flu cases in Great Britain doubled last week, and the country is literally on the brink of a pandemic," he said.

According to recent reports, Britain has registered 7,500 swine flu cases, while at least 30 people with the virus have died.

Meanwhile, Oleg Kiselev, director of the Russian Academy of Sciences' Influenza Institute, said on Monday the first batch of vaccine against the A/H1N1 swine flu will be ready in Russia by October 1.