WASHINGTON, (Reuters) – U.S. Secretary of State Hillary Clinton said on Tuesday that upcoming talks with Iran must address the nuclear issue, despite Tehran’s statement it would not bargain over its right to a nuclear program.

“We have made clear to the Iranians that any talks we participate in must address the nuclear issue head on. It cannot be ignored,” Clinton said after a meeting with Uruguayan President Tabare Vazquez.

Iran has agreed to meet on Oct. 1 with the United States and other major powers concerned about Tehran’s nuclear program.

The group, known as the P-5 plus 1, is made up of five permanent members of the U.N. Security Council — Britain, China, France, Russia and the United States — as well as Germany.

The State Department said last week it would attend the meeting, represented by Undersecretary of State William Burns. Clinton’s remarks on Tuesday were her first public comments about the decision.

The meeting is a move toward President Barack Obama’s pledge during the campaign last year to try to improve relations with Tehran through more direct contacts. The two countries have not had diplomatic ties since 1980. “This is going to be a fulfillment of President Obama’s promise of engagement,” Clinton said. “We think it is very much worthwhile but we are not going to be talking for the sake of talking, and we’re not engaging in a process that has no purpose or endpoint.”

While agreeing to the talks, Iran said it will not negotiate about its nuclear enrichment program. The United States and other major powers are concerned the program is aimed at producing a nuclear weapon, but Iran says it is for producing nuclear energy.

“Iran says it has a number of issues that it wishes to discuss with us. But what we are concerned about is discussing with them the question surrounding their nuclear program and ambitions,” Clinton said.

“We will wait to see how Iran responds in that face-to-face venue,” she said.

A bipartisan policy group on Tuesday urged Obama to increase pressure on Tehran by imposing sanctions on its energy and banking sectors and overtly preparing to use military options to stop Tehran from developing a bomb.

“Publicly signaling serious preparation for a military strike might force the Islamic Republic to recognize the costs of its nuclear defiance and encourage Tehran to engage seriously,” said the study by the Bipartisan Policy Center in Washington.

The report was written by two former U.S. senators and a retired general.