South Korea will effectively become the first of Iran's major Asian customers to halt oil purchases from July 1, when a European Union insurance ban will prevent further imports.

South Korea's largest oil refiner SK Energy will stop Iranian oil imports after the ban takes effect, two sources with direct knowledge of the matter said on Monday.

Last month, industry sources said the only other South Korean refinery that buys Iranian crude, Hyundai Oilbank, would stop imports from June.

Iran exports most of its 2.2 million barrels of crude per day to Asia, home to its four biggest buyers China, India, Japan and South Korea.

But US and EU sanctions aimed at halting Iran's nuclear programme by reducing its oil revenues have made purchases difficult, with the impending EU ban on insurance for Iranian crude shipments so far proving an effective deterrent as all Iran's Asian customers struggle to secure coverage.

The sources declined to be identified because they were not authorised to speak to the media on a topic the Korean government considers politically sensitive.

'SK Energy won't lift Iranian crude oil after lifting a 2 million barrel cargo in early June,' one of the two sources said. 'SK Energy will not import Iranian oil for July arrival.'

SK Energy had agreed to import 130,000 barrels per day (bpd) of Iranian crude this year under a long-term supply deal, while Hyundai Oilbank had agreed to import 70,000 bpd.-Reuters