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LONDON, Oct 13 (Reuters) - A looming ramp-up in U.S. sanctions on Tehran will further spook potential buyers of Iranian oil although supplies to Europe will most likely remain uninterrupted, top trading houses told the Reuters Global Commodities Summit this week.
U.S. President Donald Trump is likely to take a major step against the Iran nuclear deal on Friday, marking a more aggressive approach to Iranian activities in the Middle East.
Trump will lay out his plan in a 12:45 p.m. EDT (1645 GMT)speech at the White House, the product of weeks of internal discussions between him and his national security team.
Any big increase in sanctions will effectively leave the oil market where it was at the start of this decade, when Washington had a tough stance on Iran while the European Union still allowed trade with Tehran before beefing up sanctions in 2012.
The EU eased sanctions last year as part of a broader nuclear deal, paving the way for Tehran to increase oil trade and attract billions of dollars in investment.
"If the U.S. does decertify the nuclear deal, and raises the tension, then inevitably some people will say, well, maybe that is a business that I shouldn't be involved in," said Glencore's global head of oil, Alex Beard.
He said dealing with Iran was complex enough without any new U.S. sanctions because of a lack of dollar clearing, as the global banking system is sensitive to the U.S. view on transacting with Iran.
Glencore and Vitol, the world's No.2 and No.1 oil trading houses, have resumed dealings with Iran since last year.
The chief executive of Vitol, Ian Taylor, said he expected transactions with Iran to become more complicated although a small number of financial institutions would still facilitate trade.
"If Trump decides not to certify ... it will have some impact but I dont think the Europeans will go with him so probably the impact will be limited," he said.
Kim Gyo-hyun, CEO of Lotte Chemical, South Korea's No.2 petrochemical maker, told the summit he did not think oil prices would spike due to tighter sanctions because the world has much larger crude oil stocks than it did in 2012.
"We are not short of oil," he said.
Jeff Brown, president of energy consultant FGE, said new U.S. sanctions would complicate Iranian oil trade finance under which Tehran could attract loans guaranteed by future oil deliveries.
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For more summit stories, see (Writing by Dmitry Zhdannikov; Editing by Dale Hudson)