WASHINGTON – A key senator has written to US President Barack Obama outlining his concerns with an emerging nuclear agreement with Iran, urging him to muster the “courage” necessary to walk away should Tehran’s final proposal not meet his own set standards.Senate Foreign Relations Committee chairman Bob Corker (R-Tennessee), who brokered a compromise Iran bill between Democrats and Republicans last month that won the president’s signature, penned the letter on Monday, just 15 days ahead of a key deadline for world powers to clinch the deal.Corker’s letter referenced specific demands made by the Obama administration in recent weeks: That international inspectors be granted access across Iran “anytime” and “anywhere” that they reasonably suspect nuclear-related activities, and a satisfactory conclusion to the International Atomic Energy Agency’s investigation into the past military dimensions of Iran’s nuclear work.“If Iran tries to cross these few remaining red lines, I would urge you to please pause and consider rethinking the entire approach,” Corker writes, charging that “no sites” should be off limits to inspectors.“Walking away from a bad deal at this point would take courage, but it would be the best thing for the United States, the region and the world.”Corker has been praised by Obama – and by his press secretary, Josh Earnest – as a “good and decent man” who is “principled” in his approach to legislating with regards to Iran.But Corker was less congenial than he was critical in his letter, calling the president’s concessions to the Islamic Republic “breathtaking.” “Under your leadership, six of the world’s most important nations have allowed an isolated country with roguish policies to move from having its nuclear program dismantled to having its nuclear proliferation managed,” he writes. “I am alarmed by recent reports that your team may be considering allowing the deal to erode even further.”The White House rejected that criticism on Monday. Responding to The Jerusalem Post, National Security Council spokesman Ned Price said the Obama administration agrees with Corker “that no deal is preferable to a bad deal.”“That is why our experts, along with the experts of the P5+1 and the EU, are hard at work right now in Vienna trying to finalize the technical details and annexes of the framework understanding that we reached in April,” Price said.Diplomats from the US, Britain, France, Russia, China and Germany have been meeting with their Iranian counterparts on a constant basis ever since agreeing upon a framework for a nuclear deal in Lausanne on April 2.“The president has been clear that if the understanding and the position of Iranian officials in a final deal can’t be squared with our bottom lines, including vigorous inspections to assure that Iran isn’t cheating, and the need for a capacity to snap back sanctions in the event of a violation, then we’re not going to get a deal. Period,” Price continued.On Corker’s concern for Obama’s red line on inspections access, Price said that, while the exact details of the inspection regime are still being worked out, “we expect to come to a solution that will give us and the IAEA the assurances the international community needs with regards to access and transparency.”“If not,” he said, “as we have said all along, we will not agree to a deal that does not meet our bottom lines.”A State Department spokesman said Monday that Washington’s chief negotiator, Wendy Sherman, was likely to return to the talks at some point this week. US Secretary of State John Kerry says a self-imposed deadline for a comprehensive nuclear accord, June 30, is “critical for a lot of different reasons.” The Obama administration is concerned with a new law passed by Congress that would double the amount of time legislators would have to review and vote on a deal should the deadline be delayed past July 9.“I would like to quash any talk of a deadline extension,” Russian Deputy Foreign Minister Sergei Ryabkov said on Monday to TASS news agency, which had quoted a diplomatic source on Friday as saying a deadline extension might be needed. “Reaching a deal by the date set, by June 30, is possible.”Kerry is currently recovering from an injury he sustained to his right femur while exercising in Switzerland.But he will be attending the talks for what he hopes to be the final round, he said in an interview from his home to The Boston Globe.“Could we get an agreement? For sure,” Kerry said. “Could it fail? Yes.”Also on Monday, Russian security company Kaspersky Lab said that researchers learned the Duqu 2.0 virus had redirected computer traffic by using a legitimate digital certificate from Taiwan’s Hon Hai, also known as Foxconn.The research followed a report last week that the sophisticated computer virus was used to hack into hotels where the Iran nuclear talks took place. Foxconn customers have included many of the world’s biggest electronic makers, including Apple, Blackberry, Google, Huawei and Microsoft.Kaspersky revealed its initial findings in a report last week in which it said it found the virus in conferencing equipment at three European hotels used in talks involving Iran and six world powers, among other targets.Reuters contributed to this report.