(Updates with details of stop at border)
* Kim's train arrives at Russian border city
* Kim, Putin meeting expected in Vladivostok
* Nuclear standoff on agenda: Kremlin aide
By Hyonhee Shin and Maria Vasilyeva
SEOUL/VLADIVOSTOK, Russia, April 24 (Reuters) - North Korean leader Kim Jong Un crossed the border into Russia on Wednesday by train for his first trip there, aimed at galvanising support from President Vladimir Putin while nuclear talks with Washington are in limbo.
Kim is expected to project himself as a serious world player at his first meeting with the Russian leader on Thursday and at the same time seek assistance from a key ally to ease economic pressure brought on by U.S. and international sanctions.
The young leader will meet Putin in the Russian Pacific port of Vladivostok, with the nuclear stalemate with the United States topping the agenda, Kremlin aide Yuri Ushakov said.
"In the last few months the situation around the peninsula has stabilised somewhat, thanks in large part to North Korea's initiatives of stopping rocket testing and closing its nuclear test site," Ushakov told reporters.
"Russia intends to help in any way possible to cement that positive trend."
The armoured train carrying Kim Jong Un stopped at the railway station in the settlement of Khasan after crossing the border into Russia.
Kim, wearing a black overcoat and black fedora hat, descended from the train using a set of portable wooden steps, television footage showed.
He was greeted by girls in Russian national costume carrying bouquets of flowers, and was offered bread and salt, a traditional Russian gesture of welcome for honoured guests.
He then toured the Russian-Korean Friendship House located at the station, built ahead of a 1986 visit by his late grandfather Kim Il Sung, the founding leader of North Korea, who died in 1994, Russia's RIA news agency reported.
As he sat down for brief discussions with Russian officials, a photograph of his late father and previous North Korean leader, Kim Jong Il, was positioned on the table between the two delegations.
The North's official KCNA news agency reported earlier on Wednesday that Kim had departed for Russia accompanied by key aides including Foreign Minister Ri Yong Ho and veteran nuclear negotiator Choe Son Hui.
Kim is seeking to rally support from Moscow after his second meeting with U.S. President Donald Trump in Vietnam in February broke down over differences about demands for Pyongyang to denuclearise and for Washington to drop sanctions.
Kim would hope to get a break from crushing sanctions through his unprecedented summit with Putin but that is likely to prove elusive, analysts say.
Kim's top security and protocol aides were seen making final checks around Vladivostok station, according to South Korea's Yonhap news agency. His chief of staff Kim Chang Son and sister Kim Yo Jong were also spotted in the Far Eastern city earlier this week, South Korean media reported.
Vladivostok is the major Russian city to the northeast of the North's border with Russia, which can be reached by train, Kim's preferred mode of international transport.
Conspicuously absent from the reported entourage was Kim Yong Chol, who had led talks with U.S. Secretary of State Mike Pompeo. Kim Yong Chol had been a prominent presence during the leader's four trips to China and two summits with Trump.
U.S. nuclear envoy Stephen Biegun visited Moscow last week for talks with his counterpart Igor Morgulov, which a U.S. State Department official said would continue "to bridge any gaps on the way forward."
"The United States and the international community is committed to the same goal - the final, fully verified denuclearisation of North Korea," the official said, when asked about the Kim-Putin summit.
"It is Chairman Kim's commitment to denuclearisation upon which the world is focused," he said.
Artyom Lukin, a professor at Far Eastern Federal University in Vladivostok, said Kim would want to be seen as a world leader who is not too caught up in ongoing dealings with Washington, Beijing or Seoul.
The school's campus is expected to be venue for the summit.
"As for Russia, the Putin-Kim summit will reaffirm Moscow's place as a major player on the Korean peninsula. This meeting is important for Russian international prestige," he said.
Putin previously held a summit with Kim Jong Un's father and predecessor, Kim Jong Il, in 2002, who also met in 2011 with Dmitry Medvedev, Putin lieutenant who was then president.
The sports complex at the university was closed on Tuesday and workers were seen bringing in furniture, a Reuters TV crew at the site reported. Security guards at the entrance to the campus were searching vehicles as they drove in. (Reporting by Hyonhee Shin and Joyce Lee in SEOUL, Vladimir Soldatkin in MOSCOW, and Maria Vasilyeva in VLADIVOSTOK Additional reporting by Josh Smith in SEOUL, Maxim Rodionov in MOSCOW, and David Brunnstrom in WASHINGTON Editing by Jack Kim and Michael Perry and Catherine Evans)
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