Najib Razak
Malaysian Prime Minister Najib Razak delivers a speech at the opening of the Asean summit in Kuala Lumpur on Nov. 21, 2015. Reuters/Olivia Harris

KUALA LUMPUR (Reuters) - Malaysian anti-corruption officials questioned Prime Minister Najib Razak on Saturday in an investigation into deposits of funds totaling 2.6 billion ringgit ($615.53 million) into his bank accounts that have prompted calls for his resignation.

The Malaysian Anti-Corruption Commission (MACC) said in a statement that Najib cooperated with its officers during the meeting, which lasted two-and-a-half-hours.

A graft scandal erupted around Najib in July when the Wall Street Journal reported that investigators focused on state fund 1Malaysia Development Berhad (1MDB) had found that funds had been transferred into Najib's bank accounts.

Critics have accused the government of dragging its feet on the investigation and have called for Najib to step down due to his failure to fully explain where the money came from, why it was paid, or how it was used.

The MACC said on Thursday that it would be recording Najib's statement in connection with graft allegations at SRC International, a firm linked to 1MDB, and the funds in his account.

Najib, who chairs the 1MDB advisory board, has denied wrongdoing or taking any money for personal gain. The MACC has said earlier that the money was a political donation from an unidentified Middle Eastern benefactor.

The government has repeated that explanation in parliament, but most Malaysians, not just the prime minister's critics, remain dissatisfied with that answer, and noted his failure to take legal action against the Wall Street Journal.

The fund is also being investigated by law enforcement agencies in Switzerland, Hong Kong and the United States, media and sources have said.

The controversy has battered Malaysian markets with the ringgit losing about a quarter of its value to become Asia's worst-performing currency this year.

The MACC statement said it will keep the public informed of developments.