The U.S. economy posted its third consecutive month of weak job growth, complicating President Barack Obama's re-election prospects and turning up the pressure on the Federal Reserve to do more to help the economy.

U.S. employers added 80,000 jobs in June, barely better than the 77,000 they added in May. The monthly report from the Labor Department provided the clearest evidence yet that job growth has slowed sharply from earlier this year. The U.S. gained just 225,000 jobs in the past three months combined, making it the...