"It's been a relatively mixed start to trading in Europe on Friday and the US is on course to post small losses at the open, as the focus shifts from central banks back to trade," noted Craig Erlam senior market analyst at Oanda trading group.
Trump was Friday due to unveil a final list of Chinese imports that would face punishing tariffs, fanning fears of a trade war as Beijing warned that it could swiftly strike back.
The EU on Thursday meanwhile approved a raft of tariffs targeting US goods.
In Friday trading, the single currency recovered versus the dollar, one day after it was hammered by the ECB's announcement that was accompanied by a cut in the central bank's eurozone growth outlook, citing rising protectionism and global trade fears.
Confirmation that the ECB would end its crisis-era bond-buying stimulus provided only little support as that announcement had been widely expected.
The Federal Reserve had on Wednesday said that it would likely hike US rates twice more this year and four times in 2019, highlighting an increasing divergence between the two central banks.
Bank of Japan head Haruhiko Kuroda meanwhile on Friday defended its decision to press ahead with the country's ultra-loose monetary policy.
After a two-day meeting, the BoJ said it would retain its current framework, pointing to a disappointing lack of progress towards its longstanding 2.0 percent inflation target.
The single currency's slump Thursday had sent European stocks rallying the same day as a cheaper euro boosts the bloc's exporters.
And while the Nasdaq hit another record on Wall Street overnight, US stocks were generally choppy as fears grow that Trump will announce tariffs on billions of dollars worth of Chinese imports.
Those worries filtered through to Asia and Europe, where stock markets were fluctuating ahead of the weekend.
In London, shares in British engines maker Rolls-Royce soared 9.27 percent to 964.60 pence.
Fresh from announcing 4,600 job cuts, Rolls said it was now "well placed" to beat its cash flow target of £1.0 billion ($1.3 billion, 1.14 billion euros) by 2020.
Shares in supermarket Tesco, Britain's biggest retailer, meanwhile jumped 1.9 percent to 254.50 pence after the company reported solid first-quarter sales.