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FOREX-Sterling plunges vs dollar on Brexit fears; yen up broadly

* Dollar hits nearly three-week low against yen

* Safe-haven yen, Swiss franc well bid

* Norwegian crown falls to one-month low against dollar (Updates prices, adds quote)

NEW YORK, Feb 24 (Reuters) - Sterling tumbled to a seven-year low against the dollar on Wednesday on heightened fears of a possible British exit from the European Union, while mixed risk appetite drove the yen broadly higher.

The British pound fell below $1.39 for the first time since March 2009 on persistent concerns that a June 23 referendum could lead to a “Brexit.”

“Some drivers in the market today are U.S.-based and others international, like sterling being hit by concerns of a Brexit,” said Win Thin, global head of emerging market currency strategy at Brown Brothers Harriman in New York.

The pound last changed hands at $1.3924, down 0.6 percent.

“The euro is also getting dragged down a bit by the EU concerns, so if you’re looking for a safe haven you’re probably ... more likely to choose the yen,” said Rabobank currency strategist Jane Foley.

The yen gained against most currencies as oil prices and British exit fears drove interest in the currency. Despite oil prices rising 3 percent on strong U.S. gasoline demand offsetting worries over record-high crude stockpiles, some traders continued to bet the market will turn lower again on OPEC’s stubbornness in not cutting output.

Appetite for riskier assets was largely weak, boosting demand for currencies such as the Swiss franc and the yen. The yen tends to struggle in times of increased risk appetite because it is often used to fund investments in riskier, but higher-yielding currencies.

In times of market stress, investors typically sell those riskier assets and buy back the Japanese currency.

The euro hit a nearly three-year low against the yen . The dollar meanwhile hit a two-week low of 111.040 yen, taking it close to a 15-month low of 110.85 hit earlier in the month. It last traded at 111.760.

“Oil back in the red has given the dollar a boost against some currencies, but it’s all about the safety bid yen,” said Joe Manimbo, senior market analyst at Western Union Business Solutions in Washington.

The Swiss franc gained, pushing the dollar down 0.3 percent on the day at 0.9880 franc.

Oil-rich Norway’s crown took a heavy beating among developed-world currencies, falling to a one-month trough against the dollar and also shedding 1.73 percent against the yen. The dollar was last up 0.8 percent at 8.6744 crowns. (Additional reporting by Jemima Kelly in London; Editing by Meredith Mazzilli and James Dalgleish)

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