By Chris Hogg BBC News, Tokyo

Such high-level public criticism of the prince is unusual

The Grand Steward of the Imperial Household Agency, Shingo Haketa, used a news conference to reveal his unusually frank advice for the Crown Prince.

A year ago the emperor mentioned that he had not had many opportunities to meet his granddaughter, Princess Aiko.

Crown Prince Naruhito responded that he would try harder.

Mr Haketa's latest announcement was unusual, although perhaps not surprising.

He revealed that there was still a problem, and that he had taken the crown prince and his family to task for not visiting his parents often enough.

He said he had raised the issue with the crown prince on several occasions.

Now he has gone public with his criticism.

Whispers

So little information about the imperial family is released here that an announcement like this always causes a stir.

Japan's imperial household is portrayed in the gossip columns and society pages as a rigid, traditional institution.

The emperor and his family, it is whispered, are told what to do and when to do it by courtiers determined to preserve the majesty of the institution.

The crown prince's wife, Princess Masako is ill, and cannot carry out royal duties.

The illness is thought to have been caused by the strain of adapting to the strict rules imposed by her minders in the palace since she married into the imperial family.