Bluntly describing the Pacific islands as an "inseparable" part of Russia's territory and a strategic Russian region, Medvedev also ordered an expansion of its presence on the remote archipelago.
His comments represented a drastic sharpening of Moscow's rhetoric in the dispute with Tokyo after Japan's Prime Minister Naoto Kan called Medvedev's unprecedented visit to the islands in November an "unforgivable outrage".
The remarks are also sure to create an icy atmosphere when Japanese Foreign Minister Seiji Maehara visits Moscow on Friday for previously scheduled talks with his Russian counterpart Sergei Lavrov.
"The additional weapons which will be deployed there must be sufficient and modern to ensure the security of these islands which are an inseparable part of the Russian Federation," Medvedev said.
"We will make every necessary effort to strengthen our presence on the Kuril islands. This is our strategic region," he said at a meeting with Russia's ministers of defence and regional development shown on state television.
"Ensure that all the necessary decisions are carried out, the deliveries (of weapons) are realised and all the necessary reorganisational measures are fulfilled," Medvedev told Defence Minister Anatoly Serdyukov.
Serdyukov, who also angered Japan when he visited the islands last week, replied that the defence ministry would review what additional arms were needed on the Kurils and would report back at the end of February.
"We will prepare a programme by the end of the month. Now we understand what weapons need to be there. We will take a decision by the end of month," Serdyukov was quoted as saying.
A defence ministry source told the ITAR-TASS news agency that the Mistral class warships Russia is buying from France would be used by the Russian Pacific Fleet "including for the protection of the South Kurils".
The deputy head of the defence committee for Russia's lower house of parliament, Igor Barinov, said Medvedev's announcement was a response to "anti-Russian hysteria" in Japan.
"This decision is mainly of a political nature and tells Japan that there is going to be no revision of the results of World War II and it will cool hotheads in Tokyo," he told the RIA Novosti news agency.
The Kurils, which lie just north of Japan's Hokkaido island, have been controlled by Moscow since they were seized by Soviet troops in 1945 but their status remains a major problem in Moscow-Tokyo relations.
The dispute surrounds the southernmost four islands -- known in Russian as Iturup, Shikotan, Habomai and Kunashir -- which are still claimed by Tokyo and collectively known in Japan as the Northern Territories.
Japan does not contest Russia's sovereignty over the northernmost islands but has repeatedly demanded the return of the other four. Serdykov last week angered Japan by visiting Iturup and Kunashir.
The row also prevented Russia and Japan from signing a peace treaty to formally end World War II and stymied attempts to bring bilateral economic relations to their full potential.
The islanders -- buffeted by storm winds and often battling fog -- eke out a tough existence with fishing the main industry and Medvedev called for greater tourism and foreign investment.
"The main thing is that the people who live there should feel they are no worse off than those on the mainland," he said.
Russian foreign ministry spokesman Alexander Lukashevich said ahead of Maehara's visit that now was "the perfect time to return our relations to their normal track."
But he added: "First and foremost, we expect our Japanese colleagues to fundamentally change their attitude towards Russia."
