TOKYO, Aug 8 - Japanese Emperor Akihito, 82, in a rare video address to the public on Monday, said he worried that age may make it difficult for him to fully carry out his duties, remarks seen as suggesting the elderly monarch wants to abdicate.

In nationally televised remarks, Akihito also said there were limits to reducing the emperor's duties as the "symbol of the state", the status accorded him under Japan's post-war constitution.

Public broadcaster NHK reported last month that Akihito, who has had heart surgery and been treated for prostate cancer, wanted to step down in a few years - a move that would be unprecedented in modern Japan.

Once considered divine, the emperor is defined in the constitution as a symbol of the state and the unity of the people, and has no political power.

Akihito stopped short of saying outright that he wanted to abdicate, which could be interpreted as interfering in politics.

"When I consider that my fitness level is gradually declining, I am worried that it may become difficult for me to carry out my duties as the symbol of the state with my whole being, as I have done until now," he said.

Akihito is said to feel strongly that an emperor's full performance of his duties is integral to his constitutional role, experts say.

Opinion polls show the vast majority of ordinary Japanese sympathise with the emperor's desire to retire, but such a step would need changes to the law.

Akihito has recently been cutting back on official duties, with his heir, 56-year-old Crown Prince Naruhito, taking his place.

There were limits to how far that could go, he said on Monday. He also seemed to cast doubt on whether it was appropriate to use a current system that would allow Naruhito to take over as regent if his father were incapacitated.

"Even in such cases (of a regency), however, it does not change the fact that the emperor continues to be emperor until the end of his life, even though he is unable to fully carry out his duties as the emperor," Akihito said.

Prime Minister Shinzo Abe told reporters that, in view of the emperor's age and the burden of his official duties, it was necessary to consider what steps could be taken.

The idea of abdication has sparked opposition from Abe's conservative base, which worries that debate on the imperial family's future could widen to the topic of letting women inherit and pass on the throne, anathema to traditionalists.

Naruhito has only one daughter. Since only males can inherit the Chrysanthemum Throne, the throne after Naruhito would pass to his brother, Prince Akishino, and then to nine-year-old nephew Hisahito.

Other conservatives worry that devoting political energy to discussing abdication could sidetrack Abe's push to revise the U.S.-drafted pacifist constitution, which many conservatives see as a symbol of Japan's humiliating defeat in World War Two.

Akihito took the throne after the death of his father, Hirohito, in whose name Japan fought the war.

He has sought to soothe the wounds of the conflict in Asia during trips overseas and tried to bring the monarchy closer to the people.

It was the second time Akihito had addressed the public in a video message, the first after a massive earthquake, deadly tsunami and nuclear crisis hit northeast Japan in March 2011.