SEOUL (AFP) - North Korea said on Monday that its titular head of state would attend a World War II anniversary in Russia this week, after leader Kim Jong Un cancelled his much-anticipated trip to the Moscow event.

Kim Yong Nam, the president of the North's rubber-stamp parliament, will participate in the May 9 ceremony to mark the 70th anniversary of the Soviet victory over Nazi Germany, state-run news agency KCNA said.

Moscow had invited Kim Jong Un and the young leader had initially accepted to go on what would have been his first trip abroad since coming to power after the death of his father Kim JongIl in December 2011.

But Kim pulled out last week, citing "internal North Korean issues."

The reason for the cancellation triggered widespread speculation, with theories ranging from domestic instability to Russia's refusal to come up with an arms deal incentive.

Some analysts suggested Kim simply did not feel ready to attend an event at which a number of other world leaders would be present, including China's Xi Jinping.

Kim Yong Nam, 87, has frequently travelled overseas as North Korea's representative head of state - most recently to last month's Asia-African Conference in Jakarta.

The Kim dynasty has ruled impoverished and isolated North Korea for more than six decades with an iron fist and pervasive personality cult.

Since assuming power, Kim Jong Un has received several high-ranking Chinese officials but has yet to travel overseas or hold a single summit with a foreign leader.