Israel's National Security Minister Itamar Ben-Gvir apologised on Tuesday after his son implied in an online post that US President Joe Biden had Alzheimer's disease.

Shuvael Ben Gvir wrote that it was "important to raise awareness" about the degenerative brain condition, "which is the most common cause of cognitive decline and dementia in older people".

The post on X, formerly Twitter, was written above a photograph of Biden, who is 81 and seeking re-election, with renewed focus from political rivals on his age.

Shuavel Ben Gvir's post was later deleted but his father wrote on the same platform that his "beloved son" had committed a "serious error" and that he "deeply disapproved" of it.

"The United States of America is our great friend and President Biden is a friend of Israel," he wrote in Hebrew.

There was no place for such "derogatory" comments, he said, adding: "I apologise for my son's words."

In recent days, Ben-Gvir has himself criticised Biden for not giving Israel sufficient support in the war with Gaza militants.

His outburst against Biden came after Washington took the rare move of imposing sanctions on four Israeli settlers following rising violence against Palestinian civilians in the occupied West Bank.

Ben-Gvir himself lives in a settlement.