The China-based source told local Korean news agency Yonhap that the North has given "a positive response" to Russia's invitation for Kim to attend a ceremony marking the 70th anniversary of the Soviet victory over Nazi Germany.
The source spoke on condition of anonymity, although Yonhap gave no reason.
Russian President Vladimir Putin is also known to have asked along other key regional figures, including South Korea's Park Geun-hye, China's Xi Jinping, and Japan's Shinzo Abe - all of whom lead countries involved in the Six Party Talks that North Korea abandoned in 2009.
If Kim does attend the May 9 ceremony, it would represent his first trip abroad since succeeding his father Kim Jong-il, after he died in December 2011.
Significantly, China's Xi is also yet to visit North Korea since assuming his country's presidency nearly two years go.
But Xi did find time last year for a trip to South Korea, leading some analysts to speculate about a possible fracture in the traditional Pyongyang-Beijing alliance over issues such as the North's 2013 nuclear test in defiance of the international community.
North Korea has also been seen to be improving ties with Russia in recent months, with senior officials from both sides exchanging visits.
If Putin was to bring Kim and Xi together in May, Yonhap's source suggested that "China would feel uncomfortable with such a situation."
But Beijing has been giving out warm signals to Pyongyang of late, including sending a birthday message to Kim last week.
Chinese foreign ministry spokesperson Hong Lei also emphasized their "traditional friendship" at a recent media briefing, as he signaled China's intention to improve relations with North Korea.