VLADIVOSTOK, Russia (Reuters) - Radiation levels rose slightly in Russia's Far East on Tuesday but stayed within normal levels, officials said, as Japan struggled to cope with the worst nuclear accident since the 1986 Chernobyl disaster.
Radiation levels in Vladivostok, a city of 600,000 people some 800 km (500 miles) northwest of Japan's Fukushima nuclear plant, were 1 microroentgen per hour higher at 0400 GMT (12 a.m. ET) than six hours previously, the regional emergencies ministry said.
Russia's military said it was on alert to evacuate people if required from Russia's Sakhalin island, whose southernmost tip is visible from northern Japan, and the Southern Kuril island chain which is at the heart of a territorial dispute with Japan, Interfax news agency reported.
Called the Northern Territories by Japan, the Southern Kuril islands are inhabited by Russians and one of the islands, Tanfilyeva, is just 6 km (4 miles) from Japan's coast.
Sakhalin island holds Russia's biggest proven gas reserves in the Far East.
Japan warned radiation levels had become "significantly" higher around a quake-stricken nuclear power plant after explosions at two reactors.
But the Emergency Ministry for Russia's Far East, a large swathe of Russia home to 6.5 million people which faces Japan to its east, said it expected the winds to change in their favor.
"Eastern winds will blow for the next several days, and the air flows (from the pollution area) will move over the Pacific Ocean, away from the Russian Far Eastern coast," said ministry spokeswoman Yekaterina Potvorova.
She said radiation was being monitored across 71 sites in the Far East. Russian flagship airline Aeroflot would continue direct flights as normal to Tokyo, a spokeswoman said.
Japanese Prime Minister Naoto Kan urged people within 30 km (18 miles) of the facility north of Tokyo to remain indoors and conserve power, underscoring the dramatic escalation of Japan's nuclear crisis, the world's most serious since Soviet Ukraine's Chernobyl in 1986.
(Additional reporting by Alexei Anishchuk, Writing by Amie Ferris-Rotman, editing by Guy Faulconbridge and Jon Boyle)