For a Reuters live blog on U.S., UK and European stock markets, click LIVE/ or type LIVE/ in a news window.

April 24 (Reuters) - U.S. stock index futures fell on Thursday, with a brief equity rally fizzling out as investors assessed the latest twists and turns in the Trump administration's erratic trade policy, and a bevy of mixed corporate results.

Wall Street jumped for a second consecutive session on Wednesday on signs the White House was open to de-escalating trade tensions with China and reducing sweeping tariffs, and after President Donald Trump stepped back from his attacks on Federal Reserve Chairman Jerome Powell.

Treasury Secretary Scott Bessent said high tariffs between the U.S. and China were not sustainable, but also added that a move to reduce levies would not come unilaterally.

On Wednesday, the Trump administration said in a Federal Register post that it had launched a probe into whether imports of medium- and heavy-duty trucks and parts for them pose a national security risk, a likely precursor to tariffs.

However, the Financial Times reported that the president was planning to exempt carmakers from some of his tariffs.

A stream of contradictory headlines and the lack of clarity in the market illustrate the difficulty investors, companies and consumers face in assessing the impact of Trump's sweeping and often erratic changes to trade policy.

Coping with that uncertainty is a primary point of focus for the quarterly corporate results season.

On Wednesday, Southwest Airlines LUV.N became the latest U.S. carrier to withdraw its financial forecast due to trade war uncertainty, sending its shares down 4%.

Markets have been rattled over the past weeks by trade tensions and Trump's attacks on Powell. All three major indexes are in the red year-to-date and the S&P 500 is down over 12% from its February record high.

At 5:35 a.m. ET, Dow E-minis 1YMcv1 were down 234 points, or 0.59%, S&P 500 E-minis EScv1 were down 26.75 points, or 0.5% and Nasdaq 100 E-minis NQcv1 were down 126.25 points, or 0.67%.

Shares of automakers Ford F.N and General Motors GM.N lost about 1% each in premarket trading.

Shares of International Business Machines IBM.N slumped 7.6% after the company said 15 of its government contracts were shelved under a cost-cutting drive by the Trump administration.

Software firm ServiceNow NOW.N, on the other hand, leapt 9.2% after beating first-quarter profit estimates.

Investors will watch further trade developments, as well as a busy day of results from industry heavyweights including Procter & Gamble PG.N, Merck MRK.N and Alphabet GOOGL.O for further direction.

March durable goods and existing home sales data, as well as weekly jobless claims, will also be scrutinized for more clues on the economic outlook.

Minneapolis Fed President Neel Kashkari is also scheduled to speak later in the day.

(Reporting by Lisa Mattackal in Bengaluru; Editing by Shinjini Ganguli)

((LisaPauline.Mattackal@thomsonreuters.com;))