The largest players on the international scene may seek further UN sanctions against Iran for its failure to respond to a proposal to end the standoff over its nuclear program.

"We agreed in the absence of a clear, positive response from Iran [that] we have no choice but to pursue further measures against Iran," U.S. State Department spokesman Gonzalo Gallegos told reporters Monday.

In mid-July, six large countries — China, the U.S., Russia, Britain, France and Germany — gave Iran two weeks to respond to the latest plan to get it to stop enriching uranium.

The plan would enable Iran to continue to develop a civil nuclear program, but would stop the enrichment that could give the country a nuclear weapon. Iran has said it is not trying to develop nuclear weapons.

Iran failed to meet the two-week deadline for a response, Gallegos said. Iran's top nuclear negotiator told the European Union's foreign policy head that Iran will respond on Tuesday, he said.

The six countries, including five permanent members of the UN Security Council, had offered Iran an package of incentives to modify its nuclear program. Germany is not a member of the council.

Senior diplomats from the six held a conference call before the announcement.

Gallegos did not say how the six would respond if Iran replied Tuesday.

The Security Council approved a third round of sanctions against Iran in March.

With files from the Associated Press