MOSCOW - Japanese Prime Minister Yoshihiko Noda canceled a trip to Russia expected in mid-December, citing the health of famously tough Russian President Vladimir Putin, officials said Friday.

Noda did not specify what health problem Putin might have, but Kremlin observers for months have speculated that the Russian president, an avid sportsman, was suffering from a serious back injury.

The chatter began in September when guests and journalists at the Asia-Pacific Economic Cooperation summit in Russia's far eastern city of Vladivostok saw Putin limping. A spokesman said then that Putin had strained a muscle during a workout.

The spokesman, Dmitry Peskov, on Friday told the Interfax news agency that there had been no fixed dates for Noda's visit and that he may come to Russia in January.

Peskov said this week that rumors about Putin's back problems "were strongly exaggerated." Putin was continuing to work as always, he said.

"He doesn't intend to drop his sports workouts and that is why, like with any athlete, he can have some small pain, be it in the back, in the leg or in the arm," Peskov said in an interview with the daily Komsomolskaya Pravda. "But that never affected his working ability."

Belarusian President Alexander Lukashenko said in a Reuters interview this week that Putin's back was the reason he did not participate in a friendly hockey match.

"He adores judo," Lukashenko said of Putin, who has earned a black belt. "He raised an opponent and threw him and harmed his spine."

The Kremlin reacted to Lukashenko's statement by announcing Putin's travel schedule, which includes a trip to Turkey on Monday.

Putin, known for promoting an image as a tough and brave leader, in September flew a motorized hang glider with the intention of teaching endangered Siberian cranes a new migration path.