Barack Obama's threats to use military force to prevent Iran securing a nuclear weapon are more than idle bluffs, vice-president Joe Biden told the biggest pro-Israeli lobbying group Aipac on Monday.

Biden said that while the US preferred a diplomatic solution to the standoff with Iran, a military option remained on the table.

"The president of the United States cannot, and does not, bluff. President Barack Obama is not bluffing," Biden told the audience in Washington.