Former Malaysian premier Mahathir Mohamad said his family and friends have been visited by the income tax department as part of pressure put on him to lay off criticising Prime Minister Najib Razak.

The former mentor of Datuk Seri Najib, who has become his fiercest critic, told reporters in Jakarta yesterday: "I am being harassed at the moment. A lot of things are being done to make life very uncomfortable for me, my family and my friends. "They are being visited by the income tax department."

Dr Mahathir told a press conference: "All kinds of things have been done in order to stop me from doing anything that may affect the image of Datuk Seri Najib."

Dr Mahathir, who had warned his critics in the past against speaking poorly about the country abroad, was in Jakarta to give a public lecture titled Building Economic Independence And Clean Government to university students.

Mr Najib is slated to visit Indonesia a week later on Aug 1.

Dr Mahathir told the press conference the "wrongdoings of the current government of the Prime Minister are now known to everyone, to the whole world and to Malaysians".

The United States Justice Department last week filed a civil suit to seize US$1 billion (S$1.36 billion) in assets it believes were bought using money stolen from state fund 1Malaysia Development Berhad, which was overseen by Mr Najib.

Malaysia, Dr Mahathir said, is not democratic as Mr Najib has "seized power" over all the instruments of government.

Dr Mahathir, 91, resigned from Umno in February amid the 1MDB scandal engulfing Mr Najib. He formed the Save Malaysia campaign in March to agitate for Mr Najib's ouster, and campaigned for the opposition last month in two by-elections.

He plans to form a new political party. He said yesterday: "We don't know whether we will succeed or not but certainly you have to try something. If you don't do anything, of course you will not succeed."