HANOI (Reuters) -Russian President Vladimir Putin accepted an invitation from his Vietnamese counterpart to soon visit Vietnam as the two met on the sidelines of China's Belt and Road Forum in Beijing, Vietnamese state media reported.

Vietnam remains one of Russia's closest partners in Asia, ties that were developed during the Soviet era, and Hanoi is a major buyer of Russian weapons.

Vietnam's President Vo Van Thuong invited Putin to "soon" visit the country and "Putin happily accepted the invitation," Vietnam News Agency, the state's official newswire, reported late on Tuesday.

No practical preparation was under way "yet" as there was no date set for the possible visit, one Russian diplomat said, adding that Putin also invited Thuong to Moscow.

The two leaders met on Tuesday, the first day of the forum in Beijing, where representatives from more than 130 countries gathered to hear China's President Xi Jinping explain his vision for the next phase in his signature policy to build global infrastructure and energy networks.

The visit to Beijing was Putin's second known trip abroad since the Hague-based International Criminal Court (ICC) issued an arrest warrant for him in March. Earlier this month he had visited Kyrgyzstan, a former Soviet republic.

Like China and Kyrgyzstan, Vietnam is not a member of the ICC.

"Vietnam has always considered Russia one of its most important partners," Thuong was quoted as telling Putin, who last travelled to Vietnam in 2017.

The two agreed to deepen cooperation in multiple sectors including trade, security and defence, according to the Vietnamese state media report.

An estimated 80% of Vietnam's arsenal is made of weapons and equipment supplied by Moscow, and the two countries are discussing possible new arms deals.

Hanoi is also in talks with other countries, including the United States, over possible arms supplies.

Russia's embassy in Hanoi did not immediately reply to a request for comment.

The Southeast Asian country is pursuing a balanced foreign policy. Last month, Vietnam upgraded ties with the United States during a Hanoi visit by President Joe Biden. Vietnam is also preparing to possibly host China's Xi later this year.

(Reporting by Khanh Vu and Francesco Guarascio; Editing by Simon Cameron-Moore and Raju Gopalakrishnan)