China's imports of Iranian crude fell to their lowest level in three months in July as US and European Union sanctions targeting Teheran's oil sales went into effect.

Purchases dropped 28 percent compared with the previous month to 456,000 barrels a day, according to Bloomberg calculations from data e-mailed by the Beijing-based General Administration of Customs on Tuesday. China bought about 635,000 barrels a day of crude from Iran in June, the most in 11 months.

July was the first full month for the newest US and EU sanctions aimed at curbing Iran's nuclear program. China, the Middle East nation's largest oil customer, was granted a 180-day exemption from the US penalties after it "significantly reduced" its purchases, Secretary of State Hillary Clinton said on June 28.

"Given the prior month's big increase, this could just be short term month-to-month volatility," Gordon Kwan, the Hong Kong-based head of regional energy research at Mirae Asset Securities Ltd, said on Tuesday.