The euro fell on Thursday, putting it on track for its worst day against the dollar in a month as the European Central Bank's decision to extend its bond purchases into 2018 at a reduced rate spurred selling of the single currency.

As expected, the ECB said it would cut asset purchases to 30 billion euros from 60 billion euros starting in January while also extending the scheme by nine months to September.

Draghi, who expressed some optimism about euro zone growth at his press conference, remained cautious about the region's sluggish inflation which would need continued heavy stimulus in the form of quantitative easing (QE) from the ECB.

"With Draghi's openness to QE, it's a victory for the doves," said Marc Chandler, global head of currency strategy at Brown Brothers Harriman & Co. in New York.

The ECB's move on its bond purchases came five weeks after the Federal Reserve announced its plan to shrink its US$4.5 trillion balance sheet that had ballooned from three rounds of QE this month.

At 10:02 p.m., the euro was at US$1.1720, down 0.8 per cent from late Wednesday. It was poised for its steepest one-day loss against the greenback since Sept. 25, Reuters data showed.

The single currency was down 0.7 per cent at 133.41 yen. It retreated from 134.48 yen reached earlier on Thursday which was its strongest against the Japanese currency since December 2015.

"The market is still very long euros," Chandler said.

The latest CFTC data showed that speculative net longs in the euro have retreated from their record highs but were still near multi-year highs at above US$13 billion.

The dollar has risen in recent days on optimism about forthcoming federal tax cuts and speculation U.S. President Donald Trump would select someone to head the Fed who may want to raise interest rates at a faster pace than current Fed Chair Janet Yellen.

Trump has narrowed his search for Fed chief to Fed Governor Jerome Powell and Stanford University economist John Taylor, Politico reported on Thursday, citing one source as saying, while another counseled caution.

Yellen, Trump's economic adviser Gary Cohn and former Fed Governor Kevin Warsh are also under consideration for the post.

Trump is expected to announce his candidate before his Asian trip in early November.

An index that tracks the dollar against euro, yen and four other currencies hit a three-month high at 94.306. It was last at 94.247, up 0.6 per cent on the day.