Japan's heir to the throne asked people to be patient with his wife as she recovers from a stress-related illness.
The Crown Prince and his family have been under scrutiny
Speaking ahead of his 47th birthday, Prince Naruhito said the health of his wife, Masako, was slowly improving.
Princess Masako, 43, has been rarely seen in public since late 2003 after suffering from what the palace calls an "adjustment disorder".
The Japanese edition of a controversial book about the princess was cancelled last week after government objections.
The Japanese Foreign Ministry claimed the book, Princess Masako - Prisoner of the Chrysanthemum Throne, contained groundless claims and insulted the royal family.
Appeal for understanding
Crown Prince Naruhito said his wife was getting better but needed to regain her confidence before resuming her official duties.
"Masako is making as much effort as possible, and slowly her condition is improving," he told a group of Japanese journalists at a news conference arranged ahead of his birthday, which he celebrated on Friday.
The princess was a diplomat before marrying into the royal family
"But she still tires, and the doctors say how much she can do still must be judged on a case-by-case basis.
"I would like to ask the Japanese people to understand the situation and watch over us from a long-term perspective."
The Crown Prince said he was aware of the new unauthorised biography of his wife by Australian journalist Ben Hills but had not read it.
"Since the government is handling the issue, I will avoid further comment," he added.
Japanese publisher Kodansha Ltd said last week it had cancelled plans to bring out an edition of the book, prompting Mr Hills to accuse the authorities of censorship.
The Japanese foreign ministry had sought a formal apology and "appropriate steps" from the author over what it said were "disrespectful descriptions, distortions of facts and judgemental assertions with audacious conjectures and coarse logic".
Mr Hills refused to apologise, saying he had interviewed more than 60 Japanese, US and English sources, including former colleagues of both the Crown Prince and Princess who had never been interviewed before.
Princess Masako was a diplomat who spoke several languages and travelled the world before her 1993 marriage to Crown Prince Naruhito, heir to the Chrysanthemum Throne.
Many blame her ill health since joining the Imperial family on the pressure to produce a male heir, correspondents say.
The pressure on Princess Masako was eased when her sister-in-law had a baby boy last September, ending a succession crisis faced by the Japanese throne.