By Jessica Coacci

Factory activity continued to expand in the U.S. for the sixth consecutive month in June, according to a survey of manufacturing firms.

The Institute for Supply Management's purchasing managers' index was 53.3 last month, 0.7 percentage point lower than in May. Still, readings above 50 indicate sectoral expansion. Analysts polled by The Wall Street Journal had expected a reading of 53.9.

The new orders and production index expanded, although at a slower pace than the last reading. The prices index remained in expansion, but fell 9.1 percentage points from May's reading.

Meanwhile, the supplier deliveries index indicated slowing performance for the seventh month in a row after one month in 'faster' territory. Employment improved but still remained in contraction.

"In June, 34 percent of the comments were positive and 66 percent negative, with a 1-to-1.9 ratio of positive to negative sentiment," said Susan Spence, chair of the ISM Manufacturing Business Survey Committee.

"The conflict in Iran has impacted pricing in every category of raw materials. Especially, items that have a heavy concentration of oil in the components like our adhesives," one respondent to the survey said.

Write to Jessica Coacci at jessica.coacci@wsj.com