Talks between Russian president Vladimir Putin and North Korean leader Kim Jong Un on a possible arms deal are set to begin soon.
Mr Kim travelled for two days in an armoured train to the Vostochny space centre in Russia's far east, in what was a highly scrutinised journey.
Pyongyang fired a ballistic missile hours ahead of the meeting.
The two sanctioned regimes are expected to strike a deal that exchanges weapons for humanitarian aid.
The meeting between Mr Kim and Mr Putin is being closely watched by the US and its allies, although Pyongyang and Moscow deny that their talks are about military cooperation.
The White House said it had new information that negotiations between Russia and North Korea were on a weapons deal were "actively advancing".
National Security Council spokesman John Kirby said Russia's Defence Minister Sergei Shoigu had tried to "convince Pyongyang to sell artillery ammunition" to Russia during a recent visit to North Korea.
North Korea also wants food aid and possibly technology to help its banned nuclear and missiles programme, analysts say.
But the Kremlin said on Tuesday that the "fully fledged visit" would cover "bilateral relations, the situation in the region and in the global arena".
Mr Kim said his visit shows shows the "strategic importance" of ties between Pyongyang and Moscow, North Korean state media reported.
Kremlin spokesman Dmitry Peskov said Russia would always act in its national interest.
"The interests of our two countries are important to us, and not warnings from Washington," he was quoted as saying by Russian media.
The highly anticipated visit was expected to take place in Vladivostok where Mr Putin was hosting an economic forum - but Mr Kim's train trundled past the city and headed north towards the space centre.
The Vostochny space centre is Russia's most advanced space centre and is said to be a pet project for Mr Putin.
North Korea may seek co-operation from Russia on its space programme. Late last month, it failed a for second time to place a spy satellite in orbit after a rocket failure.
On his way to the space centre, Mr Kim made a brief stop at the border station of Khasan on Tuesday morning where he was greeted by a Russian delegation as a brass band played.
Mr Kim's train is rumoured to include at least 20 heavy bulletproof carriages. The extra weight means the train is very slow - it can only travel at around 37mph (59 km/h).
The North Korean leader's last trip abroad was to Vladivostok in 2019 for a summit with Mr Putin after the collapse of nuclear disarmament talks with the then-US president, Donald Trump.