On the week, the dollar index, a gauge of the greenback's value against six currencies was flat. Over the last two weeks, the dollar has declined about 1 percent.

Shaun Osborne, chief FX strategist, at Scotiabank said the markets have a "distinct risk-off look".

"President Trump's pronouncements on Bloomberg late yesterday, which are critical of the...EU, willing to move on Chinese tariff...are adding to market concerns broadly," he said.

The greenback rallied late Thursday in a safe-haven move after Bloomberg News reported that US President Donald Trump wanted to move ahead on a plan to impose tariffs on Chinese imports worth $200 billion next week.

That concern spilled over to the European Union after Trump also said the European Union's proposal to eliminate auto tariffs was "not good enough".

Concerns about a NAFTA deal with Canada grew after Canadian Foreign Minister Chrystia Freeland said on Friday Canada is looking for a "good deal, not just any deal."

The Toronto Star reported on Friday that Trump said in off-the-record comments to Bloomberg News this week that any trade deal with Canada would be "totally on our terms." The report, which cited remarks it had obtained, ignited more dollar buying.

By early afternoon, the dollar index was up 0.5 percent at 95.177, with the euro down 0.7 percent at $1.1589. The single currency had lost about 0.3 percent overnight, pressured by a rise in Italian government bond yields.

The Canadian dollar fell 0.7 percent versus the US dollar at 76 US cents.

The Japanese yen and Swiss franc also rose on safe-haven buying, with investors fearful about Europe's outlook. Trump has threatened to impose tariffs on cars assembled by German automakers.

Trump also threatened in an interview with Bloomberg on Thursday to withdraw from the World Trade Organization if "they don't shape up."

The cautious mood helped lift the yen, but by midday, the dollar traded little changed at 110.97 yen 110.86.

The Swiss franc rose for the sixth successive session versus the dollar, which fell 0.1 percent to 0.9670 franc.

Emerging market currencies fell. The Argentinian peso , the world's worst-performing currency this year, was down about 1 percent against the dollar, which last traded at 38.00 pesos. On Thursday, the Argentine peso tumbled 10 percent, bringing month-to-date losses to 27 percent.

Argentina's central bank voted unanimously at an emergency meeting on Thursday to raise its benchmark rate to 60 percent from 45 percent.