* Iran-U.S. tension mounts after nuclear scientist killed
* Nigerian oil union threatens to cut supply
* Coming Up: U.S. retail sales at 1330 GMT (Recasts throughout, changes dateline, previous SINGAPORE)
By Yeganeh Torbati
LONDON, Jan 12 (Reuters) - Brent crude rose more than $1 per barrel on Thursday on worries a showdown between Iran and the West in the Middle East Gulf and a strike in Nigeria could disrupt oil supplies.
Tension between the West and Iran over the Islamic Republic's nuclear programme has increased after an Iranian nuclear scientist was blown up in his car by a motorbike hitman on Wednesday, prompting Tehran to blame Israeli and U.S. agents.
Brent crude futures for February rose $1.14 to a high of $113.38 a barrel before easing to trade around 113.10 by 0940 GMT. U.S. crude oil was up 60 cents to $101.47.
Iran has threatened to retaliate against the West by closing the Strait of Hormuz, a critical shipping chokepoint for crude, if the United States and its allies impose a embargo on its oil exports.
Washington imposed additional sanctions on Iran last month and the European Union will have a meeting on Jan. 23 to decide on whether to embargo Iran's oil.
Tensions elsewhere in the Middle East have also risen, as a Frenchman became the first foreign journalist to be killed in 10 months of unrest in Syria.
"You've got the same potentially bullish factors - Iran, Syria, Nigeria - in the background," said Christopher Bellew, a broker at Jefferies Bache in London. "If it weren't for Iran, probably prices would be lower."
NIGERIAN STRIKE
As Washington steps up efforts to punish Tehran over its nuclear programme, Japan and South Korea are looking to reduce oil imports from Iran and seek alternative sources instead.
Japan, one of the biggest buyers of Iranian oil, pledged on Thursday to take action to cut its Iran crude imports after U.S. Treasury Secretary Timothy Geithner visited Tokyo to hold talks with Japanese leaders.
Another worry for oil markets is a strike and protests in Nigeria against the scrapping of a fuel subsidy. Nigeria's biggest oil union said it was ready to halt oil output if the government did not reinstate the subsidy.
Output has so far been unaffected but the threats were enough to unnerve the market as Africa's biggest oil exporter ships around 2 million barrels of crude oil per day and is a key supplier to the United States and Europe.
Worries about supply allowed investors to discount reports of sharply higher U.S. crude stocks.
Inventories surged by almost 5 million barrels to 334.65 million barrels in the week to Jan. 6, data from the U.S. Energy Information Administration (EIA) showed. This was well above estimates for an 800,000-barrel build in a Reuters poll of analysts.
Japan's commercial crude oil stocks were also up, rising almost 3 million barrels, or 3.1 percent, from the week before to 15.9 million kilolitres (99.7 million barrels), the Petroleum Association of Japan (PAJ) said.
Investors are worried the euro zone debt crisis, and a sharp slowdown in European economic growth, could curb energy demand.
A Spanish bond auction planned for Thursday promised to hold the new year's first test of investor appetite for debt from the euro zone periphery.
The debt crisis has put enormous pressure on the euro, helping boost the dollar, which often moves inversely to commodities prices.
"On the downside (we have) the strong dollar against the euro, weak economies in the euro zone, the relatively warm weather we're having in the northern hemisphere," Bellew said. (Additional reporting by Seng Li Peng in Singapore; editing by Jason Neely)
