South Korea's imports of Iranian crude in April increased 8.9% year on year to 552,884 mt, or an average 135,088 b/d, from 507,821 mt a year ago, preliminary data released Thursday by the Korea Customs Service showed.

Its April Iranian crude imports more than doubled from March imports of 274,808 mt.

South Korea paid $418.4 million for Iranian crude imports in April, up from $375.2 million a year earlier and $208 million in March.

The country's Iranian crude imports fell 50.6% year on year to 64,065 b/d in March, after doubling to 290,714 b/d in February. The February imports marked the first increase after declines for four months in a row.

In January, South Korea's crude imports from Iran fell 66.1% year on year to 64,419 b/d. In December, the imports fell 29.4% to 130,194 b/d, in November by 34.4% to 128,333 bb/d and in October by 47.4% to 98,097 b/d.

The US in November 2013 extended a six-month waiver from Iran sanctions to nine countries including South Korea, as the countries were deemed to have made significant reductions in the purchases in the previous six months. The waiver extension came after the US and five other global powers agreed in Geneva in November to a six-month pause in efforts to further reduce Iran's crude sales in return for concessions on Iran's nuclear program.

The customs data also shows that South Korea imported 9.518 million mt, or 2.33 million b/d, of crude last month, up 1.9% from 9.342 million mt in April 2013. This marked two consecutive months of year-on-year increases after seven straight months of declines.

But compared with March imports of 10.16 million mt, April imports were down 6.3%.

South Korea paid $7.69 billion for all its crude imports in April, up from $7.36 billion a year ago, but down from $8.22 billion in March.

South Korea's final trade data for April will be released later this month by state-owned Korea National Oil Corporation.