India, Feb. 5 -- Service sector growth in the U.S. unexpectedly slowed modestly in the month of January, according to a report released by the Institute for Supply Management on Wednesday.

The ISM said its services PMI dipped to 52.8 in January from a revised 54.0 in December. While a reading above 50 still indicates growth, economists had expected the index to inch up to 54.3 from the 54.1 originally reported for the previous month.

The unexpected decrease by the headline index came amid slower growth by both business activity and new orders.

The business activity index slid to 54.5 in January from 58.0 in December, while the new orders index fell to 51.3 in January from 54.4 in December.

"Poor weather conditions were highlighted by ma...