U.S. President Barack Obama criticized Republican presidential candidates Tuesday, accusing them of resorting to “bluster and big talk” on the threat from Iran.

Mr. Obama held his first news conference since November, criticizing Republican rivals for pushing for military intervention in Iran. He decried the “casualness with which some folks talk about war,” saying there is “nothing casual about it.”

Some Republican presidential candidates have warned the re-election of President Obama will ensure Iran develops nuclear weapons. And during speeches to a pro-Israel group in Washington Tuesday, three of the leading Republican presidential hopefuls all called for a tougher approach with Tehran – from placing warships along the Iranian coast to destroying Iran's nuclear facilities.

Mr. Obama defended U.S. policy on Iran, saying Tehran is facing unprecedented, crippling sanctions and that the Iranian government is now isolated. But he also stressed that U.S. and Israeli intelligence officials believe there is still a window of opportunity to resolve tensions with Iran diplomatically.

Mr. Obama also defended U.S. policy on Syria, where forces loyal to President Bashar Assad have been attacking civilian areas. He said it was only a matter of time before Mr. Assad falls from power.