“Yesterday, the president authorized the Department of Defense to equip Kurdish elements of the Syrian Democratic Forces as necessary to ensure a clear victory over ISIS in Raqqa, Syria,” she said, using the name of the umbrella group for Arab and Kurdish fighters battling the Islamic State, also known as ISIS or ISIL.

Ms. White added that the United States would take steps to ensure that Turkey did not face “additional security risks.”

There was no immediate comment from the Turkish government, which considers the Kurdish force to be terrorists, and it remains to be seen whether the assurances the Trump administration is offering the Turks will be sufficient to ease the concerns of President Recep Tayyip Erdogan, who is scheduled to meet with Mr. Trump in Washington next week.

The weapons that the United States will provide Kurdish and Arab fighters in the anti-Islamic State coalition include heavy machine guns, mortars, anti-tank weapons, armored cars and engineering equipment.

American military officials have said that weapons are needed to help the lightly armed Kurdish and Arab fighters cope with urban warfare in Raqqa against unyielding Islamic State militants who are equipped with car bombs and even some tanks they captured from the Syrian Army.

To address Turkish concerns that the arms might be used against their forces one day, the supply of weapons and ammunition will be limited to what the Kurds and Arab fighters need to carry out specific operations, American officials said.

After the battle is over, an effort will be made to retrieve any excess equipment. American advisers will also monitor the weapons that are provided to the Kurds and will cut off the supply if they discover that they are being smuggled for use elsewhere or misused, United States officials said.