North Korea has positively responded to an invitation by Russian President Vladimir Putin for its leader Kim Jong-un to attend a May ceremony marking the 70th anniversary of the Soviet victory over Nazi Germany in World War II, a South Korean diplomatic source said Tuesday.

The North's positive stance over Russia's invitation of Kim, who has not made a visit to a foreign country since taking the helm of the reclusive country in late 2011, appears aimed at prompting China to try to move toward warmer relations with Pyongyang recently, the source in Beijing said on the condition of anonymity.

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 ambition and dismal human rights record.

Putin, who has been under intense pressure over the West's response over 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.

"It was confirmed that North Korea gave a positive response to the Russian invitation for Kim Jong-un," the source said.

Still, questions remain over whether Kim would choose Russia, not China, as his first destination for a foreign trip, according to the source.

Senior Chinese diplomats have privately acknowledged a "growing need to improve the relationship with North Korea" in the wake of closer ties between North Korea and Russia, said the source, who spoke with those Chinese officials.

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, Chinese President Xi Jinping paid a state visit to South Korea last year, breaking a long-standing tradition by Chinese heads of state of visiting Pyongyang before Seoul.

Xi was also invited to the May 9 ceremony in Russia.

"If Kim visits Russia and attends the ceremony, it would be an odd situation where Kim and Xi sit together at the table set by Putin. China would feel uncomfortable with such a situation," the source said.

In the latest sign that China seeks to mend fences with North Korea, Beijing publicly confirmed last week that it sent a rare message of best wishes for the birthday of Kim.

China's foreign ministry spokesman, Hong Lei, also said Beijing will "move forward" to warmer relations with North Korea based on the principle of "traditional friendship and cooperation with North Korea in keeping with the principles of carrying on the tradition."

The principle of North Korea-China relations, endorsed by the North's late leader, Kim Jong-il, and then Chinese President Jiang Zemin in 2001, had not been seen in China's official statements over the past year. (Yonhap)