Saudi Arabia's royal family gave Malaysian Prime Minister Najib Razak a $681 million gift, Malaysia's attorney general has revealed, ending months of speculation about the source of the huge personal donation.

Attorney General Mohamed Apandi Ali told an unscheduled press conference on Tuesday that he was satisfied that the funds in Najib's account were "not a form of graft or bribery" and that "no criminal offence" had been committed in relation to the funds, according to Reuters reports.

"There was no reason given as to why the donation was made to PM Najib, that is between him and the Saudi family," Reuters reported the attorney general as saying.

Dow Jones reported that the AG also told the press conference that Najib returned $620 million of the cash to his Saudi donor as it "wasn't utilized."

According to Reuters, Apandi told the press conference that there was no need for Malaysia to seek "legal assistance" from any other country in order to investigate the funds, because he had found that no offence had been committed.

In addition, the attorney general reportedly said that he was satisfied that no offence had been committed in relation to SRC International, a former subsidiary of heavily indebted state fund 1Malaysia Development Berhad (1MDB). SRC had been probed over the alleged misappropriation of fund worth $932 million.

Malaysia's anti-graft agency has said on Dec. 31 that it had sent two reports to the attorney-general's office on its investigations into 1MDB. The agency was looking at the troubled financial state of the fund, as well as transfers allegedly made from the fund to Najib's personal bank accounts.

The Malaysian PM is chairman of 1MDB's advisory board.

The Malaysian Anti-Corruption Commission (MACC) did not reveal its findings at the time or say whether any wrongdoing was involved. It would be up to the attorney to decide any further action, it had said at the time.

