Mr Putin had a warm reception last year

Mr Kim, who is reported to have a fear of flying, entered Russian territory by train early on Thursday morning en route for Vladivostock.

It is believed to be only the second time he has left North Korea since becoming leader on the death of his father.

Mr Kim and President Putin are expected to discuss American plans for a missile defence shield which Washington says is needed for protection against what it calls 'rogue states' such as North Korea.

No quick meeting

"On the invitation of Russian President Vladimir Putin, the Chairman of the Defence Committee of the Korean People's Democratic Republic, Kim Jong-il, is arriving to Russia on an official visit," Russian news agencies quoted the Kremlin as saying.

Kim Jong-il: Only his second foreign trip as leader

But it will be some time before the two men meet up.

Mr Kim is now expected to continue his journey to Moscow by rail, along some 9,288km (5,758 miles) of track, arriving in the Russian capital on 4 August for two days of talks.

Last year the North Korean leader visited China by train, a trip that remained secret until after his return home.

This will not be the first time Mr Kim and Mr Putin have met as leaders.

Hundreds of thousands of North Koreans were said to have greeted Mr Putin in the capital Pyongyang when he became the first Russian leader to visit North Korea last year.

The two men are expected to discuss military co-operation and improved transport links, as well as the American missile defence shield.

Relations between Russia and North Korea have improved since Mr Putin became Russian president.

Correspondents say Mr Putin has worked as a link between North Korea and western countries, as well as encouraging the thaw in relations between North and South Korea.