Bank of America Corp said on Friday retired Army Gen. Tommy Franks and retired Navy Adm. Joseph Prueher have resigned from its board, meaning more than a third of its board has stepped aside since late April.

The departures were effective June 17 and come as the bank tries to improve corporate governance and bolster its board's banking and financial expertise at the behest of the U.S. government and investors.

Bank of America said the departures did not result from any disagreement with the company or management. The bank did not immediately return a call seeking further comment.

In the last two months, seven directors have left what had been a 19-person board, including lead director O. Temple Sloan, a longtime supporter of Chief Executive Kenneth Lewis.

The board now has 16 members, including four new directors with banking or regulatory experience. Among these are former Federal Reserve governor Susan Bies and former Federal Deposit Insurance Corp chairman Donald Powell.

Overhauling the board is expected to increase director scrutiny of Lewis, who was stripped in April of his role as chairman after criticism over the Charlotte, North Carolina- based bank's falling share price and the January 1 acquisition of Merrill Lynch & Co.

The bank has taken $45 billion of federal bailout money, including $20 billion to help absorb Merrill. It was not among the 10 large U.S. banks that regulators allowed this week to repay their infusions from the government's Troubled Asset Relief Program.

As part of the Merrill acquisition, three Merrill directors, including Prueher, joined the board. Prueher is the first of the three to step down.

Franks joined the board in January 2006 and is a former Commander in Chief of the U.S. Central Command. He oversaw the 2003 U.S. invasion of Iraq and overthrow of Saddam Hussein.

Prueher and Franks sat on the board's audit committee.

(Reporting by Jonathan Stempel and Phil Wahba; editing by Andre Grenon)