An annual check on the Agricultural Bank of China, one of the "big four" state banks in China, had uncovered irregularities involving 51.6 billion yuan (6.45 billion US dollars) in its business in 2004, the National Audit Office announced Monday.

According to the latest audit report, "irregulate operation" was cited as a "prominent problem" for the bank.

Irregularities in deposit business involved 14.27 billion yuan, with another 27.62 billion yuan on granting loans, while the fraudulous bill issuance involved 9.72 billion yuan, the report said.

Auditors also found 157 people suspicious for economic crimes in 57 fraud cases that involved 8.68 billion yuan. Some of these cases were conspiracy set up by bank employees and outsiders, the report said.

The auditors launched the check on agricultural bank in 2005 over its 21 local branches in places such as Beijing, Tianjin, and Shanghai.