(Recasts, updates prices, adds quote, details; changes dateline)
By Maytaal Angel
LONDON, April 18 (Reuters) - Aluminium hit its highest in nearly seven years on Wednesday amid growing supply concerns in the aftermath of U.S. sanctions on Rusal, while nickel hit a three-year peak on technical factors and fears over additional Russian sanctions.
Overnight, global miner Rio Tinto flagged possible downward adjustments to its 2018 aluminium output following sanctions on its Russian partner Rusal.
Concerns over the impact of sanctions on Rusal, which began on April 6, have pushed up aluminium up 25 percent so far.
"What's happened in the last couple of weeks is unprecedented," said Macquarie analyst Vivienne Lloyd.
"Ex-China will be in a deficit of about 5 million tonnes if no Rusal material can be used. Even if you add Chinese (semi manufactured) aluminium exports to the mix, we're still in deficit of 3.3 mln tonnes ex-China if you eliminate Rusal."
Some traders and analysts were puzzled about the surge in nickel, attributing it to technical factors, although the market has been fearful recently that the U.S. sanctions could extend to hit Russia's Norilsk Nickel.
"We have seen a consistent CTA (black box fund) bid of late. Nickel exhibits the largest spec long of the complex on our estimates at 10.5 percent of open interest," broker Marex Spectron said in a note.
PRICES: Three-month aluminium on the London Metal Exchange climbed as high as $2,490 a tonne, its strongest since August 2011, and was trading at $2,489 by 1012 GMT, up 3.5 percent. Nickel was the day's outperformer, surging almost 5 percent to hit a high of $14,870, its highest since February 2015.
ALUMINA: Prices of alumina, the raw material for making aluminium, have surged after Rio Tinto said it could not fulfil supply contracts because of the sanctions on Rusal.
Broker SP Angel said the Rio statement and Rusal sanctions only exacerbate global alumina supply constraints.
"A source at a smelter ... saying 'phones have been ringing off the hook with people looking for extra metal. They are looking for any extra tonnes, even just a few hundred'."
INDONESIA EXPORTS: Indonesia exported 8,637,595 tonnes of nickel ore up to March 31, 2018.
NORNICKEL: Russia's Norilsk is in talks with battery makers over possible investment in its mining assets.
RIO TINTO: Rio last week declared force majeure on some customer contracts following the sanctions on Rusal, the world's second biggest aluminium producer.
RUSAL HALTS ORDERS: Rusal said on Tuesday it had stopped placing orders with two logistics firms that ship its exports.
JAPAN TRADERS: Major Japanese trading houses have asked Rusal to stop shipping refined aluminium and other products.
Additional reporting by Manolo Serapio Jr., editing by David Evans