New Chancellor Nadhim Zahawi has faced criticism after he took to Twitter to declare ex-Japanese Prime Minister Shinzo Abe dead despite no official confirmation.
The Tweet has now been deleted but social media users branded it "embarrassing".
It follows a gun attack on Mr Abe, who is believed to be fighting for his life after being shot twice.
One social media user wrote: "You are embarrassing yourself (and your colleagues in the UK cabinet). Wait for official Japanese announcements before you tweet something like this."
Another said: "Maybe let Japan break this news, not you? Japan still saying he’s fighting for his life."
Mr Abe is in a "grave condition" after being shot twice in the chest from behind by a gunman in an assassination attempt.
The former prime minister was on Thursday giving a public speech on the campaign trail for a national election, when two shots were heard before Mr Abe collapsed to the ground.
Public broadcaster NHK said a man armed with an apparently homemade gun opened fire. He is now in police custody.