U.S. service industries grew more than expected last month on rising optimism about the nation's economy and overall business conditions, the Institute for Supply Management said Tuesday.

The ISM's index of the non-manufacturing services sector, which covers about 90 percent of the economy, jumped to 56 percent in February, up from the previous month's 55.2 to mark the best reading since February 2012, when the index registered 56.1 percent.

Economists polled by Reuters were only expecting 55 percent, so the new reading beats the forecast. A reading above 50 indicates expansion in the sector. Purchasing and supply executives say these figures show steady growth in the non-manufacturing sector for the 38th consecutive month.

According to the NMI survey, 13 non-manufacturing industries reported growth in the month of February. The majority of respondents indicated a growing optimism about the economy's trends and overall business conditions.

The figures follow March 1 data that showed manufacturing in the U.S. accelerated from 53.1 percent in January to 54.2 percent in February.