Growth in the U.S. manufacturing sector improved in June, helped by a jump in employment, a trade group reported Wednesday. The Institute for Supply Management (ISM) said its manufacturing index rose to 53.5 last month, up from 52.8 in May and matching the highest level since January. Any reading above 50 indicates expansion in the sector, while a reading below 50 reflects contraction. Manufacturing growth has accelerated for the past two months, evidence that factories are starting to adapt and overcome the obstacles caused by a stronger U.S. dollar and cheaper oil prices, two trends that date from last autumn. The ISM measure of new orders rose slightly to 56 in June from 55.8 the previous month. Manufacturers are responding to the increased demand by hiring more workers, with the employment gauge jumping to 55.5 from 51.7, suggesting that many companies expect additional orders in the coming months and are hiring in advance. Not every element of the ISM index reflected growth, however. The measure of production fell to 54 from 54.5. Of the 18 industries surveyed, four reported contracting in June—petroleum and coal products, primary metals, plastics and rubber products, and machinery. Declining oil prices forced energy companies to reduce orders for new equipment and pipelines.