VIENNA — On Thursday, July 17, diplomats from Iran and six world powers began to negotiate the terms of an extension for an Iran nuclear deal, as Iranian negotiators expressed frustration that their Western counterparts had not responded more positively to Iran’s proposal to hold enrichment capacity steady for up to seven years.

The five permanent members of the UN Security Council plus Germany (P5+1) “must convince us on the formula” for Iran to agree to an extension, a member of Iran’s nuclear negotiating team, speaking not for attribution, told Al-Monitor.

Iran had shown flexibility in a proposal presented to US Secretary of State John Kerry this week that would have held Iran’s enrichment capacity steady for up to seven years, among other measures. But if Iran hoped the more moderate 11th hour position would launch haggling over final deal terms to meet the July 20 interim deal deadline, it was disappointed. Diplomats here indicate they are preparing for an extension of four months, until around November 20, 2014.

Kerry, while praising tangible progress in the negotiations, returned to Washington July 15 saying there was more work to be done.