Stock index futures pointed to a flat to slightly higher open on Wall Street on Wednesday following the previous session's sell-off, which was triggered by the downgrade of Greece and Portugal credit ratings, while investors awaited the Federal Reserve's interest rate decision and statement on the economy.

At 3:40 a.m. ET, futures for the S&P 500 were up 0.11 percent, Dow Jones futures were up 0.02 percent and Nasdaq 100 futures were up 0.04 percent.

In Europe and Asia, investors on Wednesday continued to reel from the downgrades, with European stocks falling 0.8 percent in morning trade following a 3.1 percent sell-off in the previous session <.EU>. In Tokyo, Japan's Nikkei average slid 2.6 percent, dragged down by exporters such as Kyocera <6971.T>, hurt by fears the euro zone's debt problems could spread <.T>.

Senate Republicans offered counter-proposals on financial regulation reform on Tuesday that seek to water down portions of a massive Democratic bill that has been under development for months.

The Fed is expected to hold interest rates near zero and repeat its vow of an extended period of very low rates at the conclusion of a two-day policy meeting. The statement is expected around 2:15 p.m. (2:15 p.m. ET) on Wednesday.

Investors were also digesting news from China, where state media reported on Wednesday the country would place a moratorium on capital raising by real estate firms as part of a broader campaign to rein in property price rises.

Oil companies will be in the spotlight after Royal Dutch Shell Plc reported a 49 percent rise in first-quarter net profit thanks to higher oil prices and an unexpected return to production growth which helped the oil major beat all analysts' forecasts.

Tech shares will also be in focus after Germany's SAP posted double-digit growth in first-quarter sales and operating profit, underscoring a rebound in corporate technology spending.

Companies reporting quarterly results on Wednesday include Sprint Nextel Corp , Dow Chemical Co , WellPoint Inc , Visa Inc , Goodyear Tire & Rubber Co , Comcast Corp and Corning .

Shares of Broadcom Corp rose 1.5 percent to $35.25 after the bell on Tuesday after the company posted first-quarter results.

U.S. stocks tumbled on Tuesday as downgrades of Greece and Portugal fueled fear about euro-zone economic stability, and a grilling of Goldman Sachs on Capitol Hill heightened the possibility of financial reform.

The Dow Jones industrial average <.DJI> dropped 213.04 points, or 1.90 percent, to 10,991.99. The Standard & Poor's 500 Index <.SPX> slid 28.34 points, or 2.34 percent, to 1,183.71. The Nasdaq Composite Index <.IXIC> lost 51.48 points, or 2.04 percent, to 2,471.47.

(Reporting by Blaise Robinson; editing by Karen Foster)