Stocks could come under more pressure Friday as investors grow anxious about the crisis in Ukraine and the state of the Chinese economy.
U.S. stock futures were little changed ahead of Friday's opening bell.
But global markets, which often lead Wall Street, were in the red as U.S. and Russian officials met in London to try to find a diplomatic solution to an increasingly tense stand-off over the fate of the Ukrainian region of Crimea.
Investors are bracing themselves for Sunday's referendum in Crimea, where voters will decide whether to break away from Ukraine and join Russia. Ukraine and the West have described the vote as illegal. They have accused Russia of violating Ukraine's sovereignty and are threatening sanctions.
Russia's benchmark share index fell more than 2%, taking losses for the year so far to nearly 19%, and the ruble weakened further against the dollar. Russian markets have been hit hard by fears that the crisis will deter foreign investment and wipe out growth this year.
Recent poor export figures from China and signs that the government may let more companies go to the wall have sparked worries about the pace of growth in the world's second biggest economy.