Russia has extended an invitation to Prime Minister Shinzo Abe to attend a ceremony in Moscow next May on the occasion of the 70th anniversary of the Allied victory over Nazi Germany in World War II, a source close to Japan-Russia relations said Sunday.

But given Japan's continued sanctions on Moscow over the Ukraine crisis, the source said, "At the moment, it has not been decided whether Prime Minister Abe will accept the invitation."

"It's ultimately the decision of the premier" who received a letter of invitation sometime in or after summer, according to the source.