The S&P 500 and Nasdaq share indexes have opened higher, lifted by technology and financial stocks, but the Dow Jones has been held back by continued weakness in Boeing shares.
It comes as investors await the Federal Reserve's policy meeting later this week for further clues on the pace of interest rate rises.
A short while ago the Nasdaq was up half a per cent at 7,724.22 points while the S&P 500 had gained 0.3% to 2,830.78. The Dow was down 0.02% at 25842.93.
Shares in Boeing have been under pressure since a crash in Ethiopia last week involving one of its planes left 149 dead. On Monday they fell around 2.7% after Ethiopia said an initial analysis of black box data showed "clear similarities" with another Boeing crash off Indonesia in October.