KUALA LUMPUR (AFP) - Malaysia's central bank said on Wednesday it had launched a "formal inquiry" into strategic development fund 1Malaysia Development Bhd (1MDB), which is struggling under a huge debt burden and suspicions of massive fraud and mismanagement.

Prime Minister Najib Razak launched the state-owned fund in 2009 but is now fighting to limit the political fallout from its precarious situation, with opponents in his ruling party calling for his ousting over the issue.

1MDB is said to be weighed down by 42 billion ringgit (S$15 billion) in debt, which has prompted warnings it could affect the country's credit rating.

Earlier 1MDB in a statement said its 42 billion ringgit of debt was accounted for and gave a breakdown of how it was used.

Najib and the company deny allegations or wrongdoing, which centre largely on murky overseas transactions.

Critics allege that hundreds of millions of dollars appears to have been siphoned off.

1MDB says all money is accounted for but it has been taken to task over accusations of incomplete or shifting explanations.

"With respect to 1MDB, a formal enquiry has commenced to examine any contravention of the Central Bank's rules and legislation," the central bank said in a statement.

It said it was taking statements from individuals involved in the governance process and obtaining information from other relevant domestic and foreign parties.

The central bank, however, stated that it does not have the power to investigate in areas such as fraud, tax evasion, corruption, cheating and criminal breach of trust.

"These will need to be pursued by other law enforcement agencies," it added.

Najib has ordered the auditor-general's office to investigate 1MDB while the public accounts committee consisting of lawmakers has also launched investigations.