Iran and the United States (US), locked in a tense standoff after the US withdrew from a nuclear deal, traded barbs Sunday the day before the US tightens sanctions against the Islamic republic.Both sides say they want to avoid going to war, but tensions have spiralled as a series of incidents, including attacks on tankers and the shooting down of a US drone by Iran in the Gulf, raised fears of an unintended slide towards conflict.On Sunday, Iran's Foreign Minister Mohammad Javad Zarif sa