Livingstone, a member of Britain's ruling Labour Party, won widespread praise for rallying Londoners after last month's bomb attacks on the city but he has frequently courted controversy.
He clashed with journalist Oliver Feingold of the Evening Standard newspaper - which has been involved in a long-running feud with the mayor - after a function in February.
When Finegold told him he worked for the Standard and tried to ask questions, Livingstone asked: "Have you thought of having treatment?" and then asked "What did you do? Were you a German war criminal?"
Finegold said he was Jewish and found the remark offensive.

Livingstone then said the reporter was "just like a concentration camp guard, you are just doing it because you are paid to, aren't you?" 

Mayor's explanation
Livingstone has maintained his remarks were not anti-Semitic and simply reflected his annoyance at a newspaper he has accused of hounding him.
The Standards Board for England said it had looked into the remarks, the subject of a complaint by a Jewish group.
"The ethical standards officer has concluded that the issue should now be considered at a hearing held by the independent Adjudication Panel for England," a spokesman said.
The adjudication panel has the power to impose sanctions ranging from a censure to a five-year ban from public office.

The board did not give a date for the hearing.