Umno supreme council member Nazri Abdul Aziz says former premier Dr Mahathir Mohamad has failed to respond to his challenge to reveal his election expenses when he was in power.

"Don't divert… Don't run away, answer the question, and stop bull****ing," Nazri said when contacted by Malaysiakini.

On Wednesday, Mahathir retorted to what he described as Nazri's accusation of him "stealing money".

"He can make those accusations and he can lodge a police report over it. (But) I have returned all gifts, including 26 cars, I had received when I was prime minister back to the government.

"You can go to Langkawi and see what I have returned. It amounts to RM1 million or more," Mahathir had said at a ceramah in Kuala Lumpur.

Nazri however argued that this did not answer the question he asked.

"I never talked about gifts, I never said I wanted to lodge a police report, and I never called him a thief, he said that himself.

"(Mahathir was prime minister) for five elections... how many billions (in election funds) did he collect, from who, how much did he spend, what was the balance, where is it now?

"That is all... Just answer those five questions... I want him to account for all the money he collected," Nazri said.

The tourism and culture minister had made the challenge in response to Mahathir's accusations that Prime Minister Najib Abdul Razak had allegedly stolen public monies to fund his 2013 election campaign.

Critics of Najib claim that the money had been diverted from the country’s troubled sovereign wealth fund 1MDB.

They cite US Department of Justice’s allegations that US$678 million had gone into the bank accounts of an individual it dubbed as ‘Malaysian Official 1’ (MO1) just prior to the 2013 polls.

Minister in the Prime Minister's Department Abdul Rahman Dahlan has said that MO1 is Najib. However, Najib has repeatedly denied misappropriating 1MDB funds.

Defending the premier, Nazri said the money was a donation from the Saudi royal family, adding that Najib had returned the bulk of the money he received.

Attorney-general Mohamed Apandi Ali had last year claimed that Najib returned US$620 million of the money to the Saudi royalty.

The DOJ however alleged that the sum instead went to Singapore bank accounts it believed to be controlled by Penang-born tycoon Jho Low, a close associate of Najib.