The number of Americans filing new applications for unemployment benefits unexpectedly rose last week, but the trend remained consistent with solid labor market momentum that could keep the Federal Reserve on track to raise interest rates this year. Initial claims for state unemployment benefits increased 4,000 to a seasonally adjusted 277,000 for the week ended Aug. 15, the Labor Department said on Thursday. A Labor Department analyst said there were no special factors influencing the data and no states had been estimated.