U.S. stock index futures point to a lower open Wednesday, as markets worldwide fret about the crisis in Egypt hurting oil prices, while fresh data from China adds to fears of a slowdown in the world's second-largest economy, and investors brace for a raft of economic data out of the U.S.

Futures on the Dow Jones Industrial Average were down 0.69 percent, futures on the Standard & Poor's 500 Index were down 0.58 percent and those on the Nasdaq 100 index were down 0.86 percent.

Investors will assess the ADP National Employment Report, which is a precursor to the closely watched government employment report due at the end of the week. The ADP report, which measures the monthly change in non-farm private employment, is due to be released at 8:15 a.m. EDT. Economists estimate private payrolls to rise by 160,000 in June from 135,000 recorded in May.

The initial jobless claims report, which measures the number of individuals who filed for unemployment insurance for the first time last week, is also due to be released by the Department of Labor at 8:30 a.m. EDT. Economists predict that claims are likely to decline to 345,000 for the week ended June 29, from 346,000 in the previous week.

Investors are also expected to focus on the Institute for Supply Management’s non-manufacturing Purchasing Managers’ Index, also known as ISM Services PMI, due at 10:00 a.m. EDT, and the Bureau of Economic Analysis’ trade deficit report for the month of April, to be released at 8:30 a.m. EDT. Economists expect the services PMI to rise to 54.0 in June from 53.7 in May, while they forecast the trade deficit to narrow to $40.1 billion in May from $40.3 billion in the prior month.

In addition, investors are expected to focus on the Mortgage Bankers Association's mortgage applications index, which is due at 7 a.m. EDT, and the Challenger Job-Cut report, which measures the change in the number of job cuts announced by employers by industry and region, is due at 7.30 a.m. EDT.

Earlier, in other markets, investors opted for caution ahead of key economic events and hints of fresh political turmoil in Portugal, and a weak Chinese service sector data that supported fears of a slowdown in China, and pulled down stocks across Europe and Asia. And, in Egypt, the ongoing political crisis stoked fears of a global supply crunch in oil, and sent prices on Wednesday to highs not seen since May 2012. 

The Stoxx Europe 600 index fell 1.11 percent, London’s FTSE 100 was down 1.60 percent, Germany's DAX-30 declined 1.60 percent and France's CAC-40 fell 1.55 percent.

Hong Kong’s Hang Seng plunged 2.48 percent while China’s Shanghai Composite index ended the day down 0.61 percent. South Korea’s KOSPI fell 1.64 percent while India’s benchmark Sensex slumped 1.47 percent.