KUALA LUMPUR -- Malaysian Prime Minister Mahathir Mohamad, who began his second stint in office Monday, is accelerating investigations into the state fund 1Malaysia Development Berhad founded by former Prime Minister Najib Razak, who is accused of siphoning millions of dollars from it.

The prime minister's office said Monday it is establishing a special team to conduct detailed criminal investigations into the case including tracking funds and cooperating with relevant agencies in the U.S., Switzerland and Singapore. Najib's role in 1MDB, where $4.5 billion is unaccounted for, is still under investigation in some countries including the U.S. and Switzerland.

There is little doubt that Najib is at the center of Mahathir's investigations. Police raided properties linked to the former prime minister last week, seizing 72 bags of jewelry and currencies, as well as 284 boxes of expensive designer handbags.

The new investigation team will be made up of the country's anti-corruption commission, the police, the attorney-general's chambers as well as the central bank. It will be co-chaired by four law experts including those who were ousted from their posts during Najib's administration as they tried to investigate the case. They include Gani Patail, former attorney general, and Abu Kassim, former chief of the anti-corruption commission.

Separately, the anti-corruption commission will summon Najib to its office on Tuesday to hear its statements.

The 1MDB scandal that came to light in 2015 was one of the key factors that moved Mahathir to come out of retirement and to lead the opposition in the general elections earlier this month. His opposition coalition Pakatan Harapan, or Alliance of Hope, had campaigned on the promise that it would reopen investigations into 1MDB.

One of Mahathir's first tasks after winning the election was to ban Najib and his wife from leaving the country. The couple had wanted to go overseas for "a short break" on May 12. Najib is under investigation overseas for $681 million found in his offshore accounts.

Najib has repeatedly denied that the money was from 1MDB and claimed instead that it was a donation from a member of the Saudi royal family. 1MDB also maintained that it had not paid any funds into the personal accounts of Najib.

The attorney-general appointed under Najib, Apandi Ali, was also removed from his position last week. During this stint, Ali had absolved Najib of any 1MDB-related wrongdoing.