Mr. Medvedev is the first Russian president to visit one of the disputed Kuril islands. The four islands lie between the Japanese island of Hokkaido and the rest of the Kuril archipelago, which is Russian territory.
The four islands are sparsely populated but grant access to prize fisheries and promising oil and gas fields. Touring day-care centers and family homes, Mr. Medvedev told residents that Russia will invest heavily to raise living standards on the islands.

“We want people to remain here,” he said at one stop. “Development here is important. We will definitely be investing money here.”

The trip immediately aggravated relations with Japan, which has long demanded that Russia return the islands. Foreign Minister Seiji Maihara said Mr. Medvedev’s presence “injures the feelings of the population of Japan,” and summoned Russia’s ambassador to deliver a note of protest.

Japanese leaders warned Russia in September that such a visit would damage bilateral relations.
Tokyo is already locked in a tense dispute with China over islands in the East China Sea. In September, its coast guard detained the captain of a Chinese fishing boat that collided with two of its vessels. The arrest sparked anti-Japanese protests in China, which is acutely sensitive about threats to its sovereignty.

Japanese authorities have sought to calm emotions, but opposition lawmakers want to release videotape of the collision, which they believe shows that that the Chinese captain was at fault.

Russian officials responded angrily to the Japanese complaints on Monday. Mikhail Margelov, head of the Federation Council’s international affairs committee, called the protests “absurd, to say the least.”
“It is important that all our Japanese neighbors and all our partners understand that talking with Russia from a threatening position is pointless,” Mr. Margelov told the Interfax news service. “Our stance cannot be changed by pressure. I am sincerely hoping that wisdom will return to Japanese political practices.”
But Mr. Medvedev’s visit to the disputed territory will convey a clear message domestically in a country increasingly focused on the 2012 presidential elections.

Mr. Medvedev is generally viewed as milder and more liberal than his mentor, Prime Minister Vladimir V. Putin, but he has taken a tough line on territorial disputes and chose to go to war with Georgia over the breakaway enclave of South Ossetia. In the 1956 declaration that reestablished ties between Russia and Japan, Russia offered to return two of the four islands after the two countries signed a peace treaty. But Japan rejected that compromise, maintaining that all four islands should be returned, and no treaty has ever been signed.

Russia’s foothold in the Kurils weakened in the 1990s, when Moscow drew down its military presence on the islands and many Russian settlers left for the mainland.The far east carries “huge” economic importance to Russia now, both because of its oil and gas reserves and transport links to Asian markets, said Elgena V. Molodyakova, an expert on the region at the Russian Academy of Sciences.

“For us, the Kuril problem is how to develop the region,” she said. “For the Japanese, the Kuril problem is a territorial dispute that can agitate their society. If they take a hard line on this, they won’t succeed.”