“There are a lot complaints against him, all of which have to be investigated,” Mr. Mahathir said of Mr. Najib. “We had to act quickly because we don’t want to be saddled with the problem of extradition from another country.”

Mr. Najib wrote on social media that he would respect the decision.

In a series of messages earlier on Saturday, Mr. Najib said he apologized “for any shortcomings and mistakes,” but did not address the scandal at the fund, 1Malaysia Development Berhad, known as 1MDB, directly in his Twitter post.

He said that he planned to “take a short break to spend time with my family,” but he did not mention news reports that said he and his wife were planning to travel to Jakarta, Indonesia, citing the leaked flight plan.

“I pray that after this divisive period, the country will unite,” he wrote as part of his posts on Twitter and Facebook. “I apologise for any shortcomings and mistakes, and I thank you, the people, for the opportunity to lead our great nation. It has been the honour of my lifetime to serve you and Malaysia.”

He has previously denied any wrongdoing in connection with 1MDB.

Malaysiakini, a news website, quoted a source close to Mr. Najib as saying that the former prime minister and his wife planned to go to Jakarta for a two-day trip but would return.