An advertisement for Bank of China in Wuhan, Central China's Hubei province, May 9, 2015. [Photo/IC]

Bank of China Ltd, the country's fourth-largest State-owned lender, denied on Tuesday it had received any formal documents from Italian prosecutors about investigations into alleged money laundering at its Milan branch.

Media reports suggested that Italian prosecutors have accused the bank along with 297 individuals－mostly Chinese citizens living in Italy－of transferring around $5.1 billion, earned illegally there, to China.

They claimed nearly a half of the money was transferred between 2006 and 2010 via the bank's Milan branch, using the Money2Money transfer service.

Reuters reported the cash was suspected not only being earned illegally but also of avoiding paying any tax, according to a formal request by the Italian prosecutors.

In a regulatory filing to the Shanghai Stock Exchange on Tuesday, the bank clarified that it requires all overseas branches to "strictly" follow the financial regulations of both China and countries in which it operates, and that all its business "must be legal".

It said it was aware of the media reports, adding that in 2012 the Italian authorities had contacted its Milan branch requesting cooperation with an investigation into funds being transferred to China.

"The bank constantly improves its anti-money laundering management and control systems, and actively fulfills its anti-money laundering duties and obligations," the bank said.

"The bank will pay close attention to any related judicial process and release information in time according to the law," the notice said.

It said it would respond to any formal request for information from the Italian authorities investigating alleged money laundering or other financial crimes at its Milan branch.

Shares of Bank of China, which are traded in Shanghai, rose 4.19 percent on Tuesday to close at 4.72 yuan (76 cents).

In April, the People's Bank of China convened a meeting on ways of improving anti-money laundering controls.