Six major nations agreed Monday to seek new sanctions against Iran over its nuclear program after the country failed to meet a weekend deadline to respond to an offer intended to defuse the dispute, the United States said. Representatives of the five permanent members of the UN Security Council and Germany decided in a high-level conference call that Iran's lack of response to an incentives package aimed at getting it to halt sensitive atomic activity left them no option other than to pursue new punitive measures, the United States said. "We are disappointed that we have not yet received a response from Iran," State Department spokesman Gonzalo Gallegos told reporters. "We agreed in the absence of a clear, positive response from Iran (that) we have no choice but to pursue further measures against Iran." The conference call among senior diplomats from the six nations took place after Iran's top nuclear negotiator Saeed Jalali told European Union foreign policy chief Javier Solana that Tehran would deliver a written response to the offer on Tuesday, Gallegos said. He would not say if sanctions would be pursued if Iran accepted the offer on Tuesday but added that any reply from Tehran would be reviewed and a determination made then on how to proceed. "Iran has a clear choice: engagement or isolation," Gallegos said. "The incentives package contained everything Iran needed to pursue a modern civil nuclear power program, which Iran's leaders claim is their aim. The pressure on Iran to comply with the demands of the international community and its (UN Security Council) obligations will only grow." The UN Security Council has already adopted three sanctions resolutions against Iran. The United States, the European Union, as well as individual E.U. members have imposed their own financial measures against Iranian entities and individuals. On July 19, the six nations - Britain, China, France, Germany, Russia and the United States - set an informal two-week deadline for Iran to either accept or reject the package economic incentives in return for curbing its uranium enrichment. The deadline passed this weekend with no clear response from Tehran. On Sunday, Iranian President Mahmoud Ahmadinejad said diplomacy was the only way out of the standoff and insisted he was serious about negotiations. Those comments came a day after he asserted his country would not give up its "nuclear rights," signaling that it would refuse demands to stop enriching uranium or at least not to expand its enrichment work. Also Saturday, Secretary of State Condoleezza Rice said the United States would have no choice "but to begin again to prepare sanctions resolutions for the (UN) Security Council" if Iran did not halt the development of its enrichment program.