As a June 30 deadline for a final nuclear deal approaches, major differences remain between Iran and world powers on several key issues including sanctions relief and UN access to Iranian sites, a senior Western diplomat said on Friday."The most difficult subjects need to be resolved in the coming days," the diplomat told reporters on condition of anonymity in the Austrian capital, where talks between the United States, Britain, France, Germany, Russia, China and Iran have entered their final phase."The questions of access and transparency, PMD (possible military dimensions) and sanctions remain extremely problematic," the diplomat added. "We can find an agreement on some points, but on major issues there are still big differences."Iran and six major powers set themselves an end-June deadline for a long-term deal that would lift sanctions crippling the Iranian economy in exchange for limits on Tehran's nuclear program that would remain in place for at least a decade. But diplomats said the talks would likely run into July.Senior Iranian negotiator Abbas Araqchi told Iranian reporters that the current negotiations were a "slow and difficult process."But despite the major obstacles to overcome, a senior US official suggested to reporters on Thursday that an agreement could be within reach."Despite these tough issues, here's really what it's all about. We can truly see a path forward that gets us to a very good agreement here. We know what the pieces of it are," the official said on condition of anonymity."