Ali Mohammadi | Bloomberg | Getty Images
The oil tanker 'Devon' prepares to transfer crude oil from Kharg Island oil terminal to India in the Persian Gulf, Iran, on March 23, 2018

Last week, Brian Hook, the State Department Representative for Iran, declined to comment on whether the U.S. will continue to make exceptions for buyers of Iran's oil.

That is one of the most critical questions in the global oil market. The U.S. will decide by May 8 whether to continue making exemptions for certain buyers of Iranian crude. In October it exempted eight countries from the sanctions that went into place last November.

Hook said the fact that forecasts show more supply than demand for 2019 should help the U.S. be more aggressive in its efforts to take Iran's exports to zero barrels. He said Iran is currently exporting from somewhere under 1 million to 1.1 million barrels a day.

Meanwhile, OPEC Secretary General Mohammed Barkindo said the Iran sanctions are creating uncertainty as OPEC attempts to balance supply and demand in the oil market by curbing its output.