Iran and six major powers have reached a historic nuclear deal, an Iranian diplomat said on Tuesday. The diplomat said it includes a compromise between Washington and Tehran that would allow UN inspectors to press for visits to Iranian military sites as part of their monitoring duties. Under the deal, Tehran would have the right to challenge the UN request and an arbitration board composed of Iran and the six world powers that negotiated with it would have to decide on the issue. Meanwhile, oil prices tumbled on Tuesday following the deal that could see an easing of sanctions against Tehran and a gradual increase in its oil exports just as Asian economies showed further signs of weakness.