The Israeli ambassador to Japan has not yet been invited to Nagasaki's annual peace ceremony, said city officials who instead sent the embassy a letter calling for a Gaza ceasefire.

The city in southern Japan this week invited dozens of countries and territories to the August 9 event on the anniversary of the US nuclear attack in 1945 that killed 74,000 people, AFP reported. 

But "as for Israel, the situation is changing day by day... so we have put sending an invitation letter on hold," mayor Shiro Suzuki told reporters on Monday.

Worries that protests could disrupt the memorial for atomic bomb victims are partly behind the decision, said Suzuki.

"Given the critical humanitarian situation in Gaza and public opinion in the international community, there are concerns about the risk of unexpected incidents during the ceremony," which should be "safe and smooth".