Nagasaki's mayor said last week that Israel's ambassador Gilad Cohen was not invited to Friday's event in the southern Japanese city because of the risk of possible protests over the Gaza conflict.

The US and British embassies said on Wednesday that their ambassadors would not take part as a result, and that their countries would be represented by lower-ranking diplomats.

Media reports said that Australia, Italy, Canada and the European Union, who together with the United States, Britain and Germany signed a strongly worded joint letter to Nagasaki's mayor last month, would follow suit.

US ambassador Rahm Emanuel will not attend "after the mayor of Nagasaki politicised the event by not inviting the Israeli ambassador", an embassy spokesperson told AFP.

Instead, Emanuel, 64, who was ex-president Barack Obama's chief of staff, will go to a separate event at a temple in Tokyo, the spokesperson said.

The British embassy said that ambassador Julia Longbottom would also not be in Nagasaki, saying that not inviting Israel "creates an unfortunate and misleading equivalency with Russia and Belarus -- the only other countries not invited to this year's ceremony".

A spokesperson for the French embassy said that its number two would attend, telling AFP that the "decision not to invite the representative of Israel is regrettable and questionable".

Nagasaki mayor Shiro Suzuki said last week that the decision not to invite Cohen was "not politically motivated" but based on a desire to "hold the ceremony in a peaceful and sombre atmosphere".

In June Suzuki said Nagasaki had sent a letter to the Israeli embassy calling for an "immediate ceasefire" in Gaza.

Cohen, who was invited to and attended a memorial ceremony on Tuesday in Hiroshima, said last week the Nagasaki decision "sends a wrong message to the world".

"As a close friend and like-minded nation of Japan, Israel has attended this ceremony for many years to honor the victims and their families," he wrote on social media platform X.

Cohen told US broadcaster CNN on Monday that the security concerns were "invented" and that he was "really surprised by (Suzuki) hijacking this ceremony for his political motivations".

In their letter to Suzuki seen by AFP, the six Western envoys had warned that if Israel was excluded "it would become difficult for us to have high-level participation at this event".

Government spokesman Yoshimasa Hayashi declined to comment on Wednesday, saying invitations were "a decision for the organiser, Nagasaki City."

A Nagasaki official in charge of the ceremony said it was "obviously better to have high-level individuals, like ambassadors themselves, taking part".

"What is important is that representatives of the countries will attend the ceremony," he told AFP.