U.S. stock index futures were lower on Tuesday after President Donald Trump's comments on potential pharma tariffs renewed worries of the impact of a trade war, while some downbeat corporate results also weighed on investor sentiment.

Trump announced a 100% tariff on movies produced outside the U.S. but offered little clarity on how the levies would be implemented. Movie and television production companies that film overseas fell in premarket trading.

U.S. stock index futures fell on Monday after President Donald Trump reignited concerns about the effects of a global trade war by introducing new tariffs, while markets awaited the Federal Reserve's monetary policy decision this week.