Swiss National Bank (SNB) Chairman Philipp Hildebrand addresses a news conference in Bern, January 9, 2012. [Photo/Agencies]

Swiss National Bank (SNB), the central bank of Switzerland formally announced the resignation of its chairman Philipp Hildebrand on Monday among controversies over alleged currency deals made by his wife.

The resignation took "immediate effect", the SNB said.

Hildebrand's resignation came as a surprise given that last Thursday the chairman of SNB said he would not resign and that he had committed no legal error.

Speaking to the press in Bern after the decision was made, Hildebrand disclosed relevant personal emails sent during the period in which his wife made the widely disputed private financial transaction.

"I have come to the conclusion that it is not possible to provide conclusive and final evidence that my wife did indeed initiate the foreign exchange transaction on the 15th August without my knowledge," the Swiss central banker admitted.

But he still insisted that he had no knowledge of his wife's transaction on that day.

As a result, Hildebrand said he had concluded that he might not, for some time, be in a position to make the kinds of tough decisions and to implement them with the same rigor and success as in the past.

The Swiss central banker said he gave up his post with great sadness.

The Bank Council of SNB, which oversees and controls its conduct of business said in a statement released after Hildebrand' s resignation that with his departure, "Switzerland is losing an outstanding central banker with excellent international connections, which have brought great benefit to our country."

The Bank Council also gave credit to Hildebrand for having successfully steered the SNB through a period of exceptional monetary policy challenges, but at the same time accepted his decision, which it said "has made in order to protect the institution."

According to the Bank Council, Vice Chairman Thomas Jordan will hold the position of chairman of the SNB Governing Board, and his vacancy will be filled as soon as possible.

To calm the market from Hildebrand's sudden resignation, assurances from the SNB soon followed.

The SNB said its current monetary policy with a minimum exchange rate of 1.20 Swiss Franc against the euro remains unchanged.

"This policy will be pursued further with the utmost determination," it added.

Swiss central bank chairman resigns