The administration has been clear to China, Iran's top oil consumer, about no additional waivers to the sanctions after the ones granted last November, one of the senior officials said.
"They've known about it, so to my knowledge that's not being contemplated,"said the official, adding that ultimately questions about any wind-down period are for the State Department. The State Department did not immediately respond to a request for comment.
Under U.S. sanctions law, importers of Iranian oil including China, India and Turkey, could be allowed a wind-down period before getting to zero oil purchases, including a short-term waiver. Any wind-down measures would be different than the 180 day exceptions the Trump administration granted in November to China and seven other importers for significantly reducing oil purchases from Iran, measures set to end in May.
China has alternative oil suppliers including the United States and Saudi Arabia said the officials, who spoke on condition of anonymity.
After the Trump administration announced on Monday its intent to sink Iran's oil exports to zero, Iran's Revolutionary Guards repeated a threat to block the Strait of Hormuz, a vital shipping route linking Middle East oil producers to markets in Asia, Europe and North America.
One of the Trump officials said such a move would hurt both Iran and its allies. "Any attempt to disrupt freedom of navigation would be debilitating to Iran first and foremost ... and then to the range of the international community ... working hard to advocate on their side," the official said.