Prices for U.S. imports and exports fell in June for the fourth straight month, a sign of cooler economic growth worldwide that could weigh on the American economy and unnerve policymakers.

Export prices fell by 0.1 percent, matching the expectation in a Reuters poll, Labor Department data showed on Thursday.

The drop probably reflects weakness in global demand which has been hit by Europe's debt crisis and slowing growth in China.

Import prices slipped 0.2 percent last month, dragged down by another month of declining costs outside of the fuels category. Petroleum prices rose 0.2 percent.

Prices for both imports and exports have fallen every month since March, the longest such streak since 2008 when the world was mired in a financial crisis.

The drop in prices last month for imported cars and other consumer goods could help some U.S. consumers. However, some economists are worried an environment of weak inflation could raise the specter of deflation. That would be very bad, as deflation entails a spiral of falling prices and wages which is very difficult for central banks to fight.

Economists polled by Reuters had expected import prices to be unchanged last month.