Turkey has steeply cut oil imports from Iran in May and June, a source at the country's sole refiner told Reuters, to avoid U.S. sanctions after official trade data showed stubbornly high imports in April.
Lower imports from Ankara will add pressure on Tehran which is struggling to sell oil as the West expands sanctions to persuade Iran to abandon its nuclear program.
A sharp drop in crude prices in May below $100 a barrel is a further blow for Tehran which is heavily dependent on oil revenues.
The EU will join the United States in imposing a total ban on imports of Iranian oil from July.
Turkey, the world's fifth largest buyer of Iranian oil, pledged in March to cut imports by 20 percent in a move similar to Iran's Asian customers such as Japan and South Korea.
Turkey's only crude buyer, refiner Tupras, has a term contract with Iran that expires in August allowing it to lift 180,000 bpd.
However, according to official trade data it bought an unusually high 270,000 bpd of Iranian crude in March and fresh data for April showed imports at 249,000 bpd.
A source at Tupras said volumes have in fact been much smaller as April data included some purchases made in March.
He added that if counted by loading dates, April imports have been just 107,000 bpd and in May they amounted to 142,000 bpd.
"The plan for June is the same -- 142,000 bpd," the source said, adding that the company planned to keep its imports at around 80 percent of contracted volumes after July.
"We are abiding by our declaration from the end of March. We're aiming to continue in July in line with June," he said.
Most European refiners have gradually stopped lifting Iranian crude ahead of the EU embargo. From July 1 Turkey will remain effectively the sole buyer of Iranian crude in Europe.
EU imports of Iranian crude fell to around 350,000 bpd in April from over 700,000 bpd last year, trade data compiled by Reuters showed.
Turkey accounted for 7 percent of Iran's crude oil exports in 2011, according to the U.S. Energy Information Administration.
Official trade data shows that in the first four months of this year, Turkey got about 58 percent of its near 6 million tonnes in crude supplies from Iran.
Iraq, its second biggest supplier, trailed far behind with 743,537 tonnes, or 45,000 bpd in the first four months.
Other suppliers were Libya, Nigeria, Saudi Arabia, Russia, Azerbaijan and Kazakhstan. In 2011, Iran provided more than half of Turkey's total crude imports at just over 18 million tonnes.