Private equity that want to buy troubled banks would have to maintain significant capital levels and promise not to “flip’’ investments for at least three years under proposals by US regulators seeking to attract money into the ailing industry.

The proposed rules, which would require private equity companies to maintain a tier one capital ratio of at least 15 per cent – three times what is typically required of other banks – for at least three years, were introduced on Thursday in spite of disagreements among regulators over whether the requirements were too strict.