US President Barack Obama cast doubt over whether negotiators in Vienna will succeed in clinching a comprehensive agreement with Iran over its nuclear program in a television interview aired Sunday.Praising Iran’s performance under the eight-month old interim agreement, the Joint Plan of Action, which froze the crisis between Iran and world powers, Obama said the US seeks a “verifiable, locktight” deal that makes sure “they don’t get a nuclear weapon.”“The question now is: Are we going to be able to close this final gap so that they can reenter the international community, sanctions can be slowly reduced and we have verifiable, lock-tight assurances that they can’t develop a nuclear weapon,” Obama said.US Secretary of State John Kerry met with Iranian Foreign Minister Mohammad Javad Zarif in Muscat, Oman, for those negotiations on Sunday, working toward a deadline terminating talks on November 24.“There’s still a big gap,” he said. “We may not be able to get there.”Speaking to Bob Schieffer of CBS News’ Face the Nation, the president also distanced himself from Iran’s leadership days after a report alleged he sent a letter to Iranian Supreme Leader Ayatollah Ali Khamenei.“Iran has influence over Shi’a both in Syria and in Iraq,” he said, acknowledging shared interest in the defeat of Islamic State in both countries.He declined to comment on the existence of a letter to the ayatollah, but insisted the US would not cooperate militarily with Iran over the extremist threat.“We are not connecting in any way” the nuclear negotiations with discussions over Islamic State, he continued.Despite diplomatic efforts on two fronts – breaking historic silence between the two capitals – a slew of policies out of Tehran prevent the US and Iran from becoming “true allies,” including Iran’s “anti-Israeli threats and behavior,” the president said.Obama spoke with Schieffer in the Oval Office marking the show’s 60th anniversary.In Jerusalem, Prime Minister Benjamin Netanyahu on Sunday warned the six world powers, including the US, against caving to Iranian demands to pursue its nuclear program, just so it can meet the November 24 deadline to conclude the deal with Tehran.“The international community faces a clear choice,” Netanyahu said. “It can cave to Iranian demands in an agreement that would be dangerous for Israel and the world. Or it can stand firm and insist that Iran dismantle its capacity to produce nuclear weapons.”Israel won’t support any agreement that allows Iran to be a threshold nuclear state, Netanyahu said.The West suspects Iran has covertly sought to develop the means to build nuclear weapons. Israel has stated those concerns outright.“The reports that we continue to get from the International Atomic Energy Agency show that Iran continues to lie and deceive the world with respect to its pursuit of nuclear weapons,” Netanyahu said Sunday, noting that Iran is ruled by a regime that calls for Israel’s destruction and denies human rights to its citizens.“We must do everything to make sure that such a regime is not armed with nuclear weapons,” he added.The Islamic Republic has said, however, that its program is entirely for peaceful purposes.The thorniest unresolved issues are Iran’s overall uranium enrichment capacity, the length of any long-term agreement and the pace at which international sanctions would be phased out, according to Western diplomats involved in the negotiations.Earlier in the day, Ali Akbar Velayati, a top aide to Khamenei, was quoted by Iranian media as saying the Islamic Republic would not abandon its nuclear “rights” but was committed to the negotiations under Khamenei’s leadership.In Muscat, negotiations at a luxury hotel between Kerry, Zarif and European Union envoy Catherine Ashton appeared to be intense. The chief diplomats met from 11:30 a.m. to 2:30 p.m., broke for lunch and consultations, and then resumed three-way talks just before 6 p.m.Kerry said last week the US and its partners were not contemplating an extension of the deadline, although he held out the possibility that negotiations could go beyond that date if major issues were agreed upon and there were only technical details to wrap up.Speaking to Iranian state television on his arrival in Muscat on Saturday night, Zarif reiterated that sanctions imposed on Iran had brought “no result” for the West.“We need to reach a solution based on mutual respect and cooperation. If the West is interested in reaching such a solution, there is possibility to find a solution and to reach an understanding before November 24,” he said.A senior Iranian official close to the talks told Reuters the participants would discuss “the gaps that are still huge, Iran’s [uranium] enrichment capacity and time frame of lifting sanctions.”Reuters contributed to this report.