NEW YORK (Reuters) - Ratcheting up pressure on the largest US bank, New York Attorney General Andrew Cuomo has subpoenaed five current or former Bank of America Corp directors to learn what they knew about Merrill Lynch & Co's problems as the companies prepared to merge.

Cuomo issued the subpoenas yesterday morning, seeking information concerning knowledge of Merrill's mounting losses, the $5.8 billion of authorised bonus payouts, and how much should be disclose to shareholders, according to a person familiar with the probe.

The person requested anonymity because the probe is ongoing. Bank of America and Cuomo's office declined to comment.

It was unclear which directors were issued subpoenas, but they include "those most likely to have been briefed the most" about the merger in November and December, the person said.

"This is a sign that Cuomo intends to hold the BofA board accountable if it was involved in the decisions, or if it took a purely passive role and didn't perform its required function as a check on management," the person said.

Most if not all directors on the board in December will likely be expected to provide testimony, the person said.

Shareholders approved the merger on December 5, and the merger closed on January 1. About half of Bank of America's board has since left the company.

Cuomo threatened to sue Bank of America officers, perhaps including chief executive Kenneth Lewis, and its lawyers over the Charlotte, North Carolina-based bank's failure to reveal essential details about the merger.

The attorney general accused the bank of withholding information about the bonus payments, Merrill's $15.8 billion fourth-quarter loss, a more than $2 billion write-down for subprime mortgages, and its right to back out of the merger

Temple Sloan, the lead director at the time of the merger and no longer a board member, was not immediately available for comment, his office said.

Walter Massey, who replaced Lewis as chairman in April, could not immediately be reached for comment.

On Monday, federal judge Jed Rakoff rejected the bank's $33 million settlement of U.S. Securities and Exchange Commission charges that it lied to shareholders about the bonuses.

Bank of America shares were up 32 cents, or 2 percent, at $17.11 in afternoon trading on the New York Stock Exchange.