By Barbara Kollmeyer, MarketWatch

MADRID (MarketWatch) -- The U.S. dollar pushed higher across the board, hitting a fresh six-year high against the yen, while the British pound found trading choppy as polling opened in Scotland for the closely watched referendum on independence.

The dollar (USDJPY) rose to Yen108.70, versus Yen108.37 in late North American trading, but tapped Yen108.87, a fresh six-year high against the Japanese currency.

The dollar soared on Wednesday against both the euro and the yen, after policy statements by the U.S. Federal Reserve and comments by Chairwoman Janet Yellen did nothing to shift the picture of a central bank moving quickly to hike interest rates after its bond-buying program ends.

In its statement, the Federal Open Market Committee kept its pledge intact to keep rates low for a "considerable time" after it halts its bond-buying program in October, but the statement was viewed as more hawkish -- hence dollar supportive -- than had been expected. (Also see Yellen highlights http://www.marketwatch.com/story/yellen-on-considerable-time-and-other-press-conference-highlights-2014-09-17.)

More easing from China gave stock futures and European stocks a lift. China's central bank made its second surprise move this week to ease monetary policy with a cut in short-term borrowing costs for banks Thursday, amid concerns the country's economy is slowing.

The euro (EURUSD) was up slightly at $1.2876, from $1.2867 seen in late North American trading. The European Central Bank said eurozone banks borrowed EUR82.6 billion ($106.9 billion) in four-year loans from its new facility aimed at spurring lending to businesses and boosting inflation from its current ultra-low levels.

That was below what analysts expected and could foster some doubts about whether the lending program will be enough to jump-start borrowing and spending in the eurozone. Kit Juckes, global macro strategist at Société Générale, said ahead of the announcement that "a number below EUR100 billion would challenge the ECB package."

Eyes on Scotland: The pound pushed up against the dollar (GBPUSD), getting a lift after data showed U.K. store prices fell 1.2% in August, the biggest drop since July 2009. The pair traded at $1.6311, up from $1.6280 seen in late North American trade.

The Scottish vote remained a key focus for the pound. As polling stations opened early Thursday, the final YouGov survey echoed others showing a close race. The research showed the "No" vote leading 52% to 48%, but YouGov's analysts said it was still too tight to call.

The pound has been battered by what was once an unthinkable possibility: that Scots would vote to separate from the U.K. Should the referendum be defeated, the pound is expected to see an immediate relief rally, said Marshall Glitter, head of global FX strategy at IronFX.

"The response is not likely to be euphoric, however, as much of the rally has already occurred since the stunning rise in the 'Yes' vote stalled a week or so ago," he said.

In what's still viewed as an unlikely event of a "Yes" vote, Glitter and other analysts said investors can expect a sharp selloff in the pound.

In other currency trading, the euro (EURJPY) rose to Yen139.98 from Yen139.33, driven by yen weakness.

The WSJ Dollar Index , a measure of the dollar against a basket of major currencies, was slightly off at 76.71.

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