MOSCOW, Sep 13 (Reuters) - North Korean leader Kim Jong Un and Russian President Vladimir Putin met for a rare summit on Wednesday (Sep 13) at which they discussed military matters, the war in Ukraine and possible Russian help for the secretive Communist state's satellite programme.

Putin showed Kim around Russia's most advanced space rocket launch site in Russia's Far East and discussed the possibility of sending a North Korean cosmonaut into space. Kim, who arrived by train from North Korea, asked detailed questions about rockets as Putin showed him around the Vostochny Cosmodrome.

After the tour, Putin, 70, and Kim, 39, held talks for several hours with their ministers and then discussed world affairs and possible areas of cooperation one-on-one, followed by an opulent lunch of Russian "pelmeni" dumplings stuffed with Kamchatka crab and then sturgeon with mushrooms and potatoes.

Kim raised a toast with a glass of Russian wine to Putin's health, to the victory of "great Russia" and to Korean-Russian friendship, predicting victory for Moscow in its "sacred fight" with the West in the Ukraine war.

"The Russian army and people will certainly win a great victory in the sacred struggle for the punishment of a great evil that claims hegemony and feeds an expansionist illusion," Kim said, raising his glass.

US and South Korean officials have expressed concern that Kim could provide weapons and ammunition to Russia, which has expended vast stocks in more than 18 months of war in Ukraine. Moscow and Pyongyang have denied such intentions.

Putin gave numerous hints that military cooperation was discussed but disclosed few details. Defence Minister Sergei Shoigu attended the talks. The Kremlin said sensitive discussions between neighbours were a private matter.

When asked by Russian media if Moscow would help Kim build satellites, Putin said: "That's why we came here."

Washington warned it would implement further sanctions over any weapons transfers by either country to the other, and said Putin was "begging" Kim for help after losing tens of thousands of troops in Ukraine.

"We have taken a number of actions already to sanction entities that brokered arms sales between North Korea and Russia, and we won't hesitate to impose additional sanctions if appropriate," US State Department spokesman Matthew Miller said at a briefing.

He called it "troubling" that Russia would discuss cooperation with North Korea on programs that potentially would violate UN Security Council resolutions.

UN Secretary-General Antonio Guterres signalled Moscow had to tread carefully.

"Any form of cooperation of any country with North Korea must respect the sanctions regime that was imposed by the Security Council," Guterres told reporters, adding that it was "extremely relevant" in the case of Russia and North Korea.

For Russia, the summit was an opportunity to needle the United States, the big power supporter of Ukraine, though it was unclear just how far Putin was prepared to go in fulfilling any North Korean wish lists for technology.

Putin said Kim now planned to visit military and civilian aviation factories in the Russian city of Komsomolsk-on-Amur and to inspect Russia's Pacific fleet in Vladivostok.

Russian Foreign Minister Sergei Lavrov will visit Pyongyang for more talks next month, the Kremlin said.