WASHINGTON: The US State Department has called on Iran to keep the straits of Hormuz and Bab Al-Mandeb open, an official said on Tuesday after the US a day earlier demanded that Iran oil buyers halt their purchases by May 1. "We call on Iran, and all countries, to respect the free flow of energy and commerce, and freedom of navigation" in the straits, the official said. Iran has said it would block the Strait of Hormuz if it was barred from using the strategic waterway through which about a fifth of oil that is consumed globally passes. The threat from an Islamic Revolutionary Guards Corps (IRGC) commander followed a US announcement on Monday that it would end exemptions granted last year to eight buyers of Iranian oil and demanding they stop purchases by May 1 or face sanctions. Oil prices have surged to six-month highs. The Strait of Hormuz, a vital shipping route linking Middle East oil producers to markets in Asia, Europe, North America and beyond, has been at the heart of regional tensions for decades. Iran has made threats to past, without acting on them.block