While a report released by the Institute for Supply Management on Thursday showed that activity in the U.S. service sector grew for the 28th consecutive month in April, the pace of growth in the sector unexpectedly slowed compared to the previous month. The ISM said its non-manufacturing index dropped to 53.5 in April from 56.0 in March, although a reading above 50 indicates continued growth in the service sector. The drop surprised economists, who had expected the index to come in unchanged.