U.S. stock index futures suggest a subdued opening to markets on Thursday, ahead of the release of non-farm employment data, factory orders, jobless claims, ISM service PMI, while policymakers and investors consider the implications of a U.S.-led military strike on Syria.

Futures on the Dow Jones Industrial Average were flat, while futures on the Standard & Poor's 500 Index were down 0.14 percent and those on the Nasdaq 100 Index were up 0.1 percent.

Investors will wait for the ADP National Employment Report, which is a measure of the monthly change in non-farm private employment, based on the payroll data of approximately 400,000 U.S. business clients, due to be released at 8.15 a.m. EDT. The index, which comes two days ahead of the official non-farm payroll report, is expected to decline to 177,000 for August, from 200,000 recorded in the previous month.

The initial jobless claims report, which measures the number of individuals who filed for unemployment insurance for the first time last week, is scheduled to be released by the Department of Labor at 8:30 a.m. EDT. Economists predict that claims are likely to decrease to 330,000 for the week ended Aug. 31, marginally down from 331,000 in the previous week.

Meanwhile, economists expect continuing jobless claims data, which measure the number of unemployed individuals who qualify for benefits under unemployment insurance, to show a marginal decrease to 2.980 million from the 2.989 million recorded in the previous week.

Investors are also likely to focus on the Institute of Supply Management's non-manufacturing Purchasing Managers’ Index, or PMI, which will be reported at 10 a.m. EDT on Thursday. The index, also known as the ISM Services PMI, which rates the relative state of business conditions, including employment, production, new orders, prices, supplier deliveries and inventories, is expected to decline to 55 in August, from 56 in July. A level above 50 represents expansion in the industry.

“While the growth rate of retail spending remains weak, the evidence from August’s regional activity surveys was mixed,” Amna Asaf, an economist at Capital Economics, wrote in a research note.

The possibility of a military attack by the U.S. on Bashar Assad's government in Syria, over its alleged use of chemical weapons against its own people, increased, after the Senate, on Wednesday night, authorized Obama to launch a limited military assault on Syria. The resolution will head to the Senate floor next week for debate and a vote.

Investors are expected to watch for factory orders data for the month of July to be released at 10 a.m. EDT. Analysts expect the data, which measures the change in the total value of new purchase orders, placed with manufacturers, to decline sharply by 3.4 percent in July, compared to the 1.5 percent increase in the previous month, according to a Bloomberg report.

In Europe, markets were trading weaker on Thursday, ahead of monetary policy decisions from the European Central Bank, which is due at 7.45 a.m. EDT, and the Bank of England's interest-rate decision, due at 7 a.m. EDT.

The Stoxx Europe 600 index fell 0.15 percent, London’s FTSE 100 was flat, Germany's DAX-30 was trading down 0.21 percent and France's CAC-40 was trading down 0.11 percent.  

In Asia, markets mostly ended mixed. Japan’s Nikkei was up 0.08 percent, while Australia’s S&P/ASX 200 ended down 0.37 percent. In China, the Shanghai Composite index ended down 0.24 percent while Hong Kong’s Hang Seng Index rallied 1.22 percent. 

South Korea’s KOSPI Composite index rose 0.96 percent, while India’s BSE Sensex was trading up 2.1 percent in late-afternoon trade.