North Korean leader Kim Jong-un could visit Russia in May, choosing Moscow as his first destination abroad over Beijing, a South Korean diplomatic source said Monday.

Russian President Vladimir Putin has invited world leaders, including Kim and Chinese President Xi Jinping, to attend a May ceremony marking the 70th anniversary of the Soviet victory over Nazi Germany in World War II.

Russian Foreign Minister Sergei Lavrov has said that Moscow received a positive signal from Pyongyang over the invitation for Kim. On Saturday, U.S. funded-broadcaster Voice of America reported, citing an email response from the Kremlin, that Kim is likely to accept the invitation.

"There is a possibility that Kim Jong-un could visit Russia in May, given the current frosty relations between North Korea and China," said the diplomatic source in Beijing.

"To my knowledge, North Korea has not given a final decision on whether to accept the Russian invitation," the source said on the condition of anonymity.

The South Korean government is "closely watching" the development between North Korea and Russia, according to the source.

North Korea is seeking to deepen both diplomatic and economic ties with Russia at a time when its political relationship with China remains frosty amid international pressure over its nuclear ambitions and dismal human rights record.

Putin, who has been under intense pressure over the conflict in Ukraine, is also eager to bolster ties with North Korea in an apparent effort against America's pivot to Asia. Putin invited Kim to attend the May 9 ceremony during a meeting with Kim's special envoy in November.

China is North Korea's main economic benefactor, but political ties between the allies remain strained, particularly after the North's third nuclear test in early 2013.

In what many analysts believe was a message to North Korea, Xi paid a state visit to South Korea last year, breaking a long-standing tradition by Chinese heads of state of visiting Pyongyang before Seoul.

Last week, China sounded positive about Kim's possible visit to Russia in May, with the Chinese foreign ministry saying, "Such exchanges between North Korea and Russia will contribute to the peace and stability of the region." (Yonhap)