TEHRAN, Iran (AP) — Iran says European nations have not responded to its offers to sell them crude oil despite having U.S. waivers.

The semi-official Fars news agency on Tuesday quoted Oil Minister Bijan Zanganeh as saying "we have called them many times, but they do not return our calls." He did not name the oil importers, but appeared to be referring to Greece and Italy, which were among eight nations granted waivers to import Iranian oil when the U.S. restored sanctions in November.

The U.S. began ramping up sanctions after President Donald Trump withdrew from Iran's 2015 nuclear accord with world powers last year. Oil exports are a key source of revenue for Iran. The temporary waivers were intended to give countries more time to comply with the sanctions.