The embattled head of the Swiss central bank, Philipp Hildebrand, announced his resignation on Monday with immediate effect after being caught up in a scandal over foreign exchange trades by his wife.

A news conference has been set for 1415 GMT, where Hildebrand will make public "certain documents," the Swiss National Bank said in a statement.

Hildebrand on Thursday had rejected criticism of foreign currency transactions by his family last year, refusing to step down and suggesting "political motives" were at work.

When he spoke publicly for the first time about the scandal, Hildebrand said he had complied with all the regulations of the central bank but conceded he had made mistakes and that banking transparency would need to be tightened.

"I acted correctly on every count," had said following days of speculation over allegations of insider trading on a dollar trade his wife made in August three weeks before the Swiss National Bank put a cap on the Swiss franc at 1.20 euro.

"So long as I have the confidence of the government and the bank council, stepping down is not an issue for me," Hildebrand, who appeared confident while fielding questions in German and French, had said.

"Looking back I made mistakes," he conceded, saying he could have reversed his wife's decision.