WASHINGTON - US economic growth was slightly weaker than initially estimated, with real gross domestic product (GDP) expanding at an annual rate of 2.5 percent in the fourth quarter of 2017, the Commerce Department said Wednesday.

The department in January estimated last quarter's growth rate at 2.6 percent. The downward revision, which was based on more complete source data, primarily reflects a slight downward revision of private investment, said the department.

Real GDP increased 2.3 percent in 2017, compared with an increase of 1.5 percent in 2016. The pace, however, was well below the 3 percent target set by the Trump administration.

The US economy picked up steam in the second and third quarter of 2017, with the growth rate surpassing 3 percent for two consecutive quarters.

The economic expansion might lose further momentum in the first quarter of 2018. Forecasting firm Macroeconomic Advisers projected on Tuesday that the GDP would increase 1.8 percent in the first quarter.