WASHINGTON (Reuters) - Vice President Joe Biden told America's biggest pro-Israel lobbying organization on Monday that President Barack Obama is "not bluffing" about the United States' determination to stop Iran from getting a nuclear weapon.

"The president of the United States cannot and does not bluff. President Barack Obama is not bluffing," he told the American Israel Public Affairs Committee (AIPAC) in a speech to its annual policy conference.

Biden said the United States was "not looking for war" and wanted peaceful negotiations with Iran, adding that there was still time and space for talks to succeed, but the "window is closing."

(Reporting by Paul Eckert; Editing by Vicki Allen)