Companies that buy Iranian crude oil must completely cut those exports by the start of November or else they will face powerful U.S. sanctions, a senior State Department official told reporters on Tuesday.

The State Department has conveyed that message to European diplomats in recent talks, the official said. The Trump administration has not yet held talks with China, India or Turkey about their purchases of Iranian crude, but it intends to pressure them to entirely cut their imports under threat of sanctions, the official added.

Oil prices spiked following the announcement, which indicates that President Donald Trump will not follow the Obama administration model of allowing countries to gradually phase out Iranian crude exports over many months. The hardline approach comes at a time when oil markets are finely balanced and crude prices have recently hit 3½-year highs.

Iran, OPEC's third biggest oil producer, exports more than 2 million barrels a day. OPEC and other oil producers including Russia agreed last week to ease production caps that have been in place for 18 months in order to prevent prices from spiking as Venezuela's output continues to sink and the U.S. sanctions on Iran's exports loom.

President Donald Trump withdrew the United States from the Iran nuclear deal in May to pursue a maximum pressure campaign. At the time, his administration gave foreign companies either 90 or 180 days to wind down their business with Iranian counterparts, depending on the type of commercial activity.

A crucial question was whether the Trump administration would follow the model President Barack Obama put in place. His administration asked buyers to cut their imports of Iranian crude by 20 percent every 180 days when it ramped up its pressure campaign against Iran.