WASHINGTON (CNN) -- Iran "continue(s) to pursue a course that would lead to (nuclear) weaponization and that is not acceptable," President Barack Obama said Tuesday.

"We have bent over backwards to say we are willing to have a constructive conversation" with Iran about its nuclear program, he said in a surprise appearance at the White House daily press briefing.

Now the United States and its allies are "developing a significant regime of sanctions that will indicate to them how alone they are," he said.

Obama said negotiations on proposed sanctions for Iran "are moving along."

But one of the difficulties of dealing with Iran, Obama added, is that "it's not always clear who is speaking on behalf of the government" in Tehran.

The president indicated there are signs Iran is still pursuing nuclear weapons.

"The door's still open" to discussions with the Iranian government, he added. But "we are going to be looking at a variety of ways" in the weeks ahead to show the Iranian regime its current approach is unacceptable, he said.

The-CNN-Wire/Atlanta
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