The country's immigration department said in a brief statement on Saturday that Najib and his wife, Rosmah Mansor, have "just been blacklisted from leaving the country".
When asked if any senior government officials would be suspended anytime soon, Dr Mahathir said: "At the moment I need to get proper information before I can act".
Cukup Pendapatan Mansuhkan GST (Enough Funds To Abolish The GST) - Berita Harian reported that the Prime Minister vehemently emphasised that the country's income will not decrease in the absence of the GST as he blamed misused funds and wastefulness as the root cause of the decrease.
After that, there were reports of around $700 million transferred from the fund to Najib's personal bank accounts.
Najib has consistently denied any wrongdoing in connection with 1MDB.
Addressing a news conference, the 92-year-old Mahathir said all government ministries had been instructed that no documents could be taken out or destroyed.
With Mahathir's campaign promise to review all infrastructure projects including the East Coast Rail Link project, keep an eye on Gamuda Bhd, IJM Corp, Malaysian Resources Corp and George Kent Malaysia Bhd.
"I was already informed that the immigration department of Malaysia doesn't allow me and my family to foreign countries".
The government of corruption-tainted prime minister Najib Razak had used ethno-nationalist populism, the suppression of free speech and gerrymandering of electoral boundaries to give greater weight to ethnic Malay voters in rural constituencies, who benefit most from state handouts, in order to prevent an opposition victory. The announcement came after calls from the organization, the linchpin of the coalition, for Najib to resign. Najib had earlier tweeted he was going to take a "short break".
"We accept the people's verdict with an open heart", Najib said. Mr Mahathir sacked Mr Anwar from his post as deputy prime minister and jailed him on a dubious sodomy charge in 1999. Anwar's daughter Nurul Izzah said her father, whose sentence ends June 8, would be released Tuesday.
"I don't consider myself as a Chinese, I am a Malaysian".
Mahathir has been prime minister of the Muslim Malay-majority nation earlier, for 22 years, governing in a tough, direct style.
Malaysian Prime Minister Mahathir Mohamad's new government will review political representation in the country's largest government-linked investment firms, including the main sovereign and state pension funds, the funds have said.