Iran's average oil exports have been 600,000 to 700,000 barrels per day (bpd) since March, an official from the budget and planning organisation said on Wednesday, defying US sanctions aimed at dropping Tehran's main source of income to zero.

Iran's oil exports have shrunk from more than 2.5 million bpd since the United States withdrew from a nuclear deal with Iran 2018 and reimposed sanctions.

"The average oil sales so far this (Iranian) year have been 600,000 to 700,000 barrels per day," Hamid Pourmohammadi told Iran's semi-official Fars news agency, without providing further details. The Iranian year began on March 20.

Iranian authorities have said Washington's "maximum pressure" policy aimed at halting Iran's oil exports have failed as Tehran has been working to get around the measures and keep exports flowing.

Citing three assessments based on tanker tracking, Reuters reported this year that Iranian oil exports had risen sharply in September, although the figures fall into a wide range of between 400,000 and 1.5 million bpd.