By Aniruddha Ghosh

(Reuters) - U.S. stock index futures fell on Tuesday on concerns that a planned visit by U.S. House of Representatives Speaker Nancy Pelosi to Taiwan could worsen tensions between the United States and China.

The latest geopolitical uncertainty comes at a time when financial markets are already dealing with the fallout from a war in Ukraine, energy crisis in Europe, soaring inflation and tightening of financial conditions.

Shares of chipmakers, which have a large exposure to China, fell in premarket trading. Qualcomm, Intel Corp, Advanced Micro Devices, Micron Technology Inc and Nvidia Corp were down between 1.3% and 2%.

The CBOE volatility index, also known as Wall Street's fear gauge, rose to 24.50 points, its highest level in a week.

At 6:58 a.m. ET, Dow e-minis were down 218 points, or 0.67%, S&P 500 e-minis were down 32.5 points, or 0.79%, and Nasdaq 100 e-minis were down 124.5 points, or 0.96%.

Markets have kicked off August on a lackluster note amid heightened fears of a global recession, after data showed factory activity weakened across the United States, Europe and Asia.

Against the backdrop of a difficult macro-economic environment, investors have become increasingly jittery about the health of corporate America.

DuPont de Nemours fell 2.7% after the industrial materials maker lowered its full-year adjusted earnings and net sales outlook.

Caterpillar Inc slid 6.9% after its quarterly sales missed market expectations due to supply-chain issues and the suspension of its Russia operations.

Pinterest Inc jumped 19.4% as the activist investor Elliott Investment Management become the largest shareholder of the digital pin-board firm.

(Reporting by Aniruddha Ghosh and Devik Jain in Bengaluru; Editing by Anil D'Silva)