The emperor of Japan is “concerned” about holding the Olympic Games during Covid-19, according to his most senior official, in a rare intervention that skirted a ban on Imperial involvement in politics.

According to remarks at a press conference reported by local media outlets, Imperial grand steward Yasuhiko Nishimura said it was his impression that the monarch was worried about the event.

The comments, made just 28 days before the games are due to begin, will be deeply unwelcome to Prime Minister Yoshihide Suga, who has decided to stage the event with stadiums at half capacity.

Imperial press conferences are highly scripted and it is unlikely Nishimura would have made the remarks without some form of authorisation from Emperor Naruhito.

Naruhito, who acceded to the throne in May 2019, has so far followed his father’s example by avoiding any political controversy, making the comments particularly unusual.

“In regard to the Olympics, the emperor is extremely concerned about the state of coronavirus infections at the present time,” said Nishimura, according to national broadcaster NHK. “Given the voices of concern among the public, I surmise he is worried about the risk of increased infections at the Olympic and Paralympic Games, for which he himself will serve as honorary patron.”

“For myself, to prevent a situation where infections increase, I would like the organising committee and related parties to do everything they can on virus countermeasures.”

The Tokyo 2020 organising committee decided this week to disregard medical advice and hold the games with a maximum of 10,000 fans or half the available capacity. Japan’s government relaxed a state of emergency in Tokyo and other big cities at the weekend.

Japan’s chief medical adviser is worried that the sight of stadiums full of fans will prompt the public to relax their guard against Covid and socialise more at a time when the Delta coronavirus variant is gaining ground.

Article 4 of the Japanese constitution is usually interpreted as prohibiting almost any comment or action by the emperor with political implications. The article, adopted after the exploitation of Imperial power by militarists during the second world war, says: “The Emperor shall perform only such acts in matters of state as are provided for in this Constitution and he shall not have powers related to government.”

Katsunobu Kato, chief cabinet secretary, signalled that the government would not treat the remarks as coming from the emperor, saying: “I acknowledge the grand steward has expressed his personal views.” Kato promised to realise “a safe and secure Olympics”.

Japanese public opinion had been swinging towards a grudging acceptance that the games will go ahead. However, the decision to allow spectators, followed by a quickly reversed suggestion that the stadiums would serve alcohol, has reignited concern about the wisdom of staging the event.