Former Malaysian prime minister Mahathir Mohamad has spoken out again against beleaguered Prime Minister Najib Razak, who is currently embroiled in a scandal involving debt-ridden state investment agency 1Malaysia Development Berhad (1MDB) and allegations that billions had been pumped into his personal accounts.

Responding to Foreign Affairs Minister Anifah Aman's criticism over his issuance of an open letter to United States paper The New York Times last month, Tun Mahathir said in his latest blog posting on Tuesday that Datuk Seri Najib had shamed the country due to the 1MDB saga.

"The person who has shamed the country is Najib and his 1MDB. Before this, the country was never ridiculed like this, with such allegations that remain unanswered until now," Dr Mahathir wrote.

Datuk Seri Anifah had said the former prime minister's act of writing to the NYT had undermined Malaysia, and was part of a personal vendetta.

Dr Mahathir, however, chided Mr Anifah, saying he had probably not read international papers before making that statement.

"The whole world knows about Datuk Seri Najib, Jho Low and 1MDB.

"This is because all the main newspapers in Washington, New York and London have written lengthy pieces up to four pages long on the 1MDB scandal, Najib and his lavish lifestyle and his close friend Jho Low and his stepson Riza Aziz that funded the obscene movie The Wolf of Wall Street," Dr Mahathir said.

He said these reports had been printed even more his criticism of Mr Najib, and Mr Anifah would have felt some shame over these reports, if he "had any sense of shame".

He added that a scandal-hit leader in any other nation would have apologised, and resigned.

"Only in Malaysia there will be those who defend a leader with no good reason, just to protect their own positions," he wrote.

His posting on the blog chedet.cc comes as six bank accounts linked to the allegations were frozen.

A special task force formed to probe the allegations stated that the order to freeze the accounts was issued on July 6, reported The Star.

Last Friday, The Wall Street Journal and the Sarawak Report website published an article quoting an "unnamed investigator", who claimed that almost US$700 million (S$946 million) of 1MDB funds had gone into Mr Najib's personal accounts.