Westpac Acting CEO Peter King (Image: AAP/Mick Tsikas)

Westpac went into damage control over the weekend, taking out ads in major newspapers apologising "unreservedly" for its 23 million alleged breaches of money laundering laws.

The advertisement appeared in News Corp and Nine newspapers on Saturday, featuring a letter from Westpac's new acting CEO Peter King admitting the bank's transaction monitoring "should have been more robust".