Wall Street remains jittery as ECB action looms

U.S. stock index futures signaled a softer open on Wednesday as investors face another day of big name tech and bank earnings, amid speculation that the European Central Bank (ECB) will announce a new stimulus package Thursday.

Major earnings to watch for on Wednesday include UnitedHealth, US Bancorp, Fifth Third before market open and American Express, eBay, SanDisk, Discover Financial, F5 Networks after the bell.

A trader works on the floor of the New York Stock Exchange.
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A trader works on the floor of the New York Stock Exchange.

Other earnings to expect include SLM, Northern Trust, Kinder Morgan, United Rentals and Xilinx.

Investors are also on standby ahead of the ECB meeting Thursday, where a full-scale bond-buying program is likely to be announced. Analysts expect the ECB Governing Council to agree on a package of at least 500 billion euros (circa 5 percent of GDP). European stocks traded flat to lower ahead of the meeting.

U.S. data on Thursday brings December housing starts figures, which are expected to show an uptick of about 1 percent month on month to around 1.04 million following a dip in November.

This would leave the number of housing starts broadly in line with the average for the second half of the year, suggesting that momentum in the sector remains soft, according to head of economic research at Daiwa Capital Markets, Chris Scicluna.

The former U.S. Treasury Secretary Larry Summers warned of weakness in the deflation-hit euro zone economy on Tuesday evening, saying that it is on the "brink of deflating" and urgently needs more stimulus, particularly from Germany, Reuters reported.

Read MoreHere's what's haunting the global economy

The first full day of the World Economic Forum in Davos, Switzerland also kicks off Wednesday, where heads of state and government as well as global business leaders are attending the event including Chinese Prime Minister Li Keqiang, French President François Hollande and German Chancellor Angela Merkel.

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In the U.K., the Bank of England voted unanimously to keep rates on hold this month for the first time since July last year. Two members of the bank's Monetary Policy Committee that voted for a rate rise in previous months said a hike now could dent the already below-target inflation rate.