WASHINGTON — The United States is deepening its involvement in the war against the Islamic State group after an unprecedented American airlift of Arab and Kurdish fighters to the front lines in northern Syria, supported by the first use of U.S. attack helicopters and artillery in the country.

The U.S. forces didn’t engage in ground combat, but the offensive suggests the Trump administration is taking an increasingly aggressive approach as it plans an upcoming assault on the extremists’ self-declared capital of Raqqa. U.S. helicopters were used to ferry rebels into combat near the Tabqa Dam on the Euphrates River.

Col. Joseph Scrocca, a spokesman for the U.S.-led military coalition that is fighting the Islamic State militants in Syria and Iraq, said it was the first time U.S. forces have airlifted local fighters into combat in Syria. An undisclosed number of U.S. military advisers were inserted with the rebels.

U.S. officials said the operation inserted Syrian Arab and Kurdish fighters behind Islamic State group lines west of Raqqa, subjecting the American personnel to a degree of risk previously avoided in Syria. The mission was focused on recapturing the dam, the nearby town of Tabqa and a local airfield.

The operation is coinciding with a potentially climactic battle for Mosul, the main Islamic State group stronghold in Iraq.