Iran's oil exports have fallen sharply since President Donald Trump said he would re-impose sanctions on Tehran earlier this year, but with waivers in hand, the Islamic republic's major buyers could scale up orders as soon as next month.

The original aim of the sanctions was to cut Iran's oil exports as much as possible, to quash its nuclear and ballistic missile programs, and curb its support for militant proxies, particularly in Syria, Yemen and Lebanon.

Washington has pledged to eventually halt all purchases of crude oil from Iran globally but for now its eight biggest oil clients — China, India, South Korea, Japan, Italy, Greece, Taiwan and Turkey — can continue imports without penalty. Crude exports contribute one-third of Iran’s government revenues.

The exemptions allow the eight countries to import at least some oil for another 180 days, and could mean the exports start to rise after November. This group of eight buyers takes as much as three-quarters of Iran's seaborne oil exports, trade data shows.

"The decision by the U.S. (to grant waivers) represents a departure, for now, from the stated aim of reducing Iran's oil exports to zero," said Pat Thaker, regional director for the Middle East and Africa at The Economist Intelligence Unit.

Japan and South Korea, both close U.S. allies, had toed the Washington sanctions line and stopped buying crude from Iran.

Japanese Trade Minister Hiroshige Seko said Tuesday that Japanese buyers of Iranian oil are expected to resume imports from the Islamic republic after the country was granted a waiver from U.S. sanctions.

Even China, locked in a bitter trade war with the United States, bowed to pressure from Washington and dialed back imports.

Trump said he wanted to go slow on the sanctions, citing concerns about causing global price spikes.

“I could get the Iran oil down to zero immediately but it would cause a shock to the market. I don’t want to lift oil prices,” he told reporters.