Malaysia's Central Bank has recommended criminal prosecutions in connection with the controversial state investment fund 1MDB.

The bank said the fund, which was set up by Malaysian Prime Minister Najib Razak, had invested nearly $1.83bn abroad without using proper procedures.

It wants the money brought back to Malaysia.

There has been a series of sensational revelations about 1MDB that have threatened Mr Najib's position.

Documents leaked in July indicated that Mr Najib received some $700m in his private accounts from entities linked to the fund. Mr Najib denies doing anything wrong. He says the money was a donation from the Middle East.

The fund has debts of 42bn ringgit ($11.5bn) and is the subject of several investigations by different authorities, including the Central Bank.

The bank's statement comes just a day after the country's attorney general, appointed to look into the matter by the prime minister, said he had seen a report of the central bank's investigation and judged that 1MDB officials had not committed any offence.

The central bank said 1MDB had gained permits for investment abroad, but these were based on inaccurate or incomplete disclosure of information.

The political scandal has drawn in the former prime minister, Mahathir Mohamad. He alleged that ruling party leaders accepted bribes and the police should take action.

Dr Mahathir and the Bersih pro-democracy movement have called for Mr Najib to resign over corruption allegations.

Tens of thousands of Malaysians have attended rallies across the country.