Spain's Caixabank said on Tuesday it would launch a full takeover bid for Portugal's BPI, paying 1.329 euros ($2) per share for the 55.9 percent of the lender it does not already own.

The cash offer, worth around 1.08 billion euros and at a 27 percent premium against the Portuguese bank's closing price on Monday, is dependent on obtaining the backing of at least 50 percent of shareholders, including its own 44.1 percent stake, Caixabank said in a statement to the market regulator.

BPI must also eliminate an existing rule capping at 20 percent of the lender's share capital the voting rights of a specific shareholder.

The buyout will hit Caixabank's fully-loaded capital ratio by 80 to 140 basis points, depending on the level of acceptance, and will produce synergies worth 130 million euros a year from 2017, the Spanish bank said.