German Chancellor Angela Merkel says Iran's response to an international proposal regarding Tehran's nuclear program is "not satisfactory."

In an interview on German television Thursday, the chancellor said Iran's response to an offer of economic incentives does not say whether Tehran will halt uranium enrichment. Iran said on Tuesday it is ready for "serious negotiations" on its nuclear program.

The United States also has said Iran's response is not sufficient.

A State Department spokesman, Gonzalo Gallegos said Thursday there is still time before the August 31 deadline for Iran to halt enrichment activities.  A U.N. Security Council resolution set the deadline.

The U.S. spokesman said if Iran does not make the right choice, the Security Council will adopt appropriate measures, such as sanctions.

France says Iran has to stop enriching uranium before talks can take place.

The State Department spokesman said the U.S. is already working with the Security Council to make sure sanctions can be adopted in what he called an expedited manner.

But Russia and China have been reluctant to punish Iran for its nuclear activities.

The United States and many of its European allies suspect Iran is planning to build nuclear weapons. Iran insists its nuclear program is strictly for peaceful purposes.