South Korea's Samsung Total Petrochemicals (STC) has revived a contract to buy Iranian oil after a year's hiatus, as thin margins in plastics make the cheap fuel from Iran hard to resist, people familiar with the deal said.

Stringent US and European sanctions aimed at reducing Iran's oil income and forcing Tehran to curb its nuclear programme have made shipping and paying for the oil hard, halving the Islamic Republic's crude exports.

The deal is a rare example of a buyer returning to the market for Iranian oil despite the obstacles arising from sanctions and efforts by Western powers to stem the flow.

After jarring interruptions in exports from Iran last year that included a halt in shipments to top consumers Japan and South Korea, importers have found ways to keep oil flowing without violating sanctions.

The allure of cheap oil and improved margins has made it worthwhile for the South Korean joint venture between two big international firms to find ways around difficulties.

The deal may save STC as much as $6.7 million in costs, according to Reuters calculations.

"The deal can be easily understood if you look at Samsung Total's financial situation," according to a government source in Seoul with direct knowledge of the matter.

The company is a joint venture between South Korea's Samsung Group and French energy giant Total.

While spokespeople at STC and the Samsung Group declined to comment, a spokesman for Total in Paris said the group complied with all legislation applicable to the group.

"STC is a South Korean company and is subject to the laws of South Korea," he said, adding that the Asian country had obtained in June last year an exemption from the United States to continue purchasing Iranian oil despite sanctions.

"Any purchase of petroleum products by any South Korean company is covered by this exemption," the spokesman added.

Asked during a news briefing in Paris if the deal broke international sanctions, French Foreign Ministry spokesman Philippe Lalliot said: "It is complex and we have to look at the legal side of it and see if it's within the parameters of the sanctions.

"What I will say is we will respect to the letter the different sanctions trains, especially as it is France that pushed for them," he added.

The European Commission had no immediate comment on the matter.

Samsung Total stopped importing oil from Iran last year as the US and European Union imposed sanctions to halt a nuclear programme the West suspects Iran may be using to develop arms. Tehran denies this. To comply with U.S. sanctions, importing countries are required to reduce purchases of Iranian oil.

Co-owner Total also stopped buying Iranian oil for its refineries to comply with EU sanctions last year.

Replacing the Iranian oil forced up Samsung Total's input costs, contributing to a fall in operating profits, sources said. Those profits fell 90 percent in the second-quarter of 2012, according to the company's regulatory filings. The company switched to more expensive Australian and Russian condensate last year, sources said.

Samsung Total had an annual contract to buy about 550,000 barrels a month of Kangan condensate until June last year, although it is unclear if it actually imported the full volume during the first half of 2012. The volume of the new contract is unclear.

Other South Korean refiners will have to import less to make way for Samsung Total's new contract if Seoul is to comply with US sanctions.

To renew six-month exceptions to sanctions granted by Washington, buyers of Iran's oil have to show continuous import cuts. South Korea's waiver is next due for review in May.

The north Asia nation slashed crude purchases from Iran 36 percent to 153,405 barrels per day (bpd) in 2012. If Samsung Total starts buying a similar-sized cargo every month, South Korea's imports from the Opec member may rise by 10,000 bpd.

Condensate imports were not included when South Korean and U.S. officials discussed cuts in Iranian crude imports, the South Korean government official said. For talks due in May, it is unclear whether Iranian condensates would be included in the crude import data or whether it would be counted separately.

"The US side may raise the issue with us when they next meet for talks if they spot higher imports of Iranian condensate," the official said. "In the talks with the United States last December, we only talked about a cut in Iranian crude oil imports. Iranian condensate was not discussed."

Samsung Total kicked off imports from Iran by buying 30,000 tonnes, or 280,000 barrels, of Kangan condensate, which will be delivered in March to the petrochemical company's plant in Daesan, the sources said.

Condensate is a light oil usually processed in a unit called a splitter to produce naphtha, to make petrochemicals.

Samsung Total is looking to diversify supply sources to feed expanded facilities. It is adding a new 140,000 bpd condensate splitter, due to start in August 2014. The company operates a 1 million tonne per year (tpy) ethylene cracker, a 90,000 bpd splitter and other petrochemical units in Daesan.-Reuters