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March 6 (Reuters) - U.S. stock index futures fell on Thursday as uncertainty about an ongoing global trade war clouded sentiment, while chip stocks took a beating after Marvell Technology's broadly in-line forecast fanned worries of slowing demand for AI infrastructure.

At 5:28 a.m. ET, Dow E-minis 1YMcv1 were down 344 points, or 0.80%, S&P 500 E-minis EScv1 were off 55 points, or 0.94%, and Nasdaq 100 E-minis NQcv1 were lower 233.25 points, or 1.13%.

Marvell MRVL.O fell 15.5% in premarket trading after the chipmaker forecast first-quarter sales in line with analysts' average estimate, which failed to excite investors who had expected stronger AI-driven growth.

Peer Broadcom AVGO.O, which is expected to report results after markets close, fell 3.4%, while Nvidia NVDA.O lost 1.6% and Advanced Micro Devices AMD.O dropped 1.5%.

Megacaps such as Microsoft MSFT.O dipped 0.8% and Meta META.O and Alphabet GOOGL.O declined 1.4% and 0.7%, respectively.

Concerns that overspending and overcapacity in the U.S. AI industry, in the face of China's cheaper DeepSeek models, have been some factors that paused Wall Street's bull rally in January. The tech-heavy Nasdaq .IXIC is now down about 9% from its record high hit in December.

Further, Alibaba's U.S-listed shares BABA.K surged 2% after the release of a new reasoning model that the conglomerate said was on par with global hit DeepSeek's R1.

On the trade front, President Donald Trump exempted automakers that comply with existing free trade agreement and sources said the negotiations were ongoing. However, Trump made it clear that he was not calling off his trade war, citing the need for more border controls.

Automakers such as General Motors GM.N, Ford F.N and Tesla TSLA.O were down over 1% after Wednesday's rise.

Against this backdrop, U.S. stocks have witnessed increased volatility over the past few sessions.

Wall Street's main indexes closed higher over 1% on Wednesday following Trump's announcement. However, the benchmark S&P 500 .SPX is down this year and the Russell 200 index .RUT has fallen nearly 6%. Futures tracking the domestically focused index RTYcv1 fell 1% on Thursday.

Multiple reports have suggested that tariff uncertainty has resulted in individuals holding back on consumption and corporate executives staying put on investment decisions, sparking concerns of an impending economic slowdown as inflation stays elevated.

A weekly report on jobless claims is due before markets open but Friday's key payrolls data will be crucial for investors trying to gauge the economy's health.

Traders now see the Federal Reserve lowering borrowing costs by 25 basis points for the first time this year in June, according to data compiled by LSEG.

Comments from policymakers Philadelphia Fed President Patrick Harker, Governor Christopher Waller and Atlanta Fed President Raphael Bostic, due later in the day, are likely to strike a cautious tone on monetary policy easing.

Zscaler ZS.O rose 4.6% after raising its fiscal 2025 revenue forecast, signaling increasing demand for its cloud-based cybersecurity services.

(Reporting by Johann M Cherian in Bengaluru; Editing by Maju Samuel)

((johann.mcherian@thomsonreuters.com;))