A senior US official said on Monday that Iran must respond to an offer presented to it by the United States, Russia, China, France, Britain and Germany by July 12 or it will face action by the United Nations Security Council.

If Iran has not responded by July 12, "then I think the pressure will be enormous on the Iranians from all the international community," Nicholas Burns, U.S. undersecretary of state for political affairs, told U.S. media.

Moreover, July 12 will be "an important date" as U.S. Secretary of State Condoleezza Rice will hold talks with the foreign ministers of Russia, China, France, Britain and Germany on Iran's nuclear issue, Burns said.

Burns said Iran has two options to choose.

"Iran could sit down on a rational basis and talk to the countries about all these issues. Or it could face another path forward, and that would be action of the Security Council," Burns said.

The United States has repeatedly urged Iran to respond to the offer designated to try to solve Iran's thorny nuclear issue in weeks rather than months, and threatened that it will seek United Nations Security Council sanctions if Iran does not show cooperation.

Iranian President Mahmoud Ahmadinejad has said Iran will make a response to the offer on Aug. 22 and the United States has dismissed this as too late.