KABUL—The U.S. military has withdrawn from the Bagram Air Field northeast of Kabul, the centerpiece of its operations in Afghanistan for nearly 20 years, as the pullout of remaining American forces speeds up amid a worsening security crisis.

U.S. officials say that all American forces, along with weaponry, vehicles and other equipment, have left Bagram, and the U.S.’s largest military installation in Afghanistan is now closed. This leaves only the coalition headquarters compound inside Kabul as the remaining American military outpost in Afghanistan, with several hundred U.S. troops assigned there.

President Biden has pledged to remove all combat U.S. forces by September, following last year’s agreement in Qatar between the Trump administration and the Taliban. U.S. officials say the pullout may be completed in July, however. Taking advantage of the American departure, the Taliban has launched a major offensive in recent weeks, capturing about one-quarter of Afghanistan’s districts.

Related Video

President Biden said he will withdraw all U.S. troops from Afghanistan by Sept. 11, marking the second time in less than two years that an American president has set a date to end involvement in the Afghan conflict -- the longest war in U.S. history. Photo: Andrew Harnik/Getty Images (Video from 4/14/21) The Wall Street Journal Interactive Edition

“We consider [the] evacuation of all U.S. forces from Bagram a positive step,” Taliban spokesman Zabiullah Mujahid said Friday on Twitter, adding that, “Afghans can move closer to peace and security with complete withdrawal of foreign forces.”

There was no public observance of the closing of the Bagram base, which was one of the first to house American forces, drones, jet fighters and special forces troops in Afghanistan after the 2001 U.S. invasion. Leaving Bagram removes most of the remaining U.S. capability to provide air support to American or coalition forces from inside the country.

SHARE YOUR THOUGHTS

What do you see in Afghanistan’s future after American troops withdraw? Join the conversation below.

From now on, air support must come from bases in Qatar or other allies in the Middle East, or from an aircraft carrier in the region, all of which are hours away from Afghanistan, diminishing the effectiveness of those resources. The worsening security situation has dictated that the U.S. military must be as inconspicuous as possible as it closes bases, removes gear and redeploys troops home, U.S. officials have said.

The top U.S. commander in Afghanistan, Army Gen. Scott Miller, remains there for now. His departure, which was expected as soon as Monday, is now postponed for at least another week, U.S. officials said, in an attempt to shore up the Afghan security forces.

Aerial porters loaded a helicopter into a military transport aircraft in Bagram on June 16.

Aerial porters loaded a helicopter into a military transport aircraft in Bagram on June 16.

Photo: sgt 1st class corey vandiver/Agence France-Presse/Getty Images

U.S. intelligence concluded in June that Afghanistan could fall within six months of American forces leaving, creating alarm within the White House. Once Gen. Miller departs, a two-star commander, Navy Rear Adm. Peter Vasey, will replace him and assume command over the residual force that will focus on protecting the U.S. Embassy in Kabul.

Despite the drawdown of all combat forces in Afghanistan, there are plans for the U.S. to retain as many as 1,000 troops assigned to the embassy to play an advisory role for the Afghan government, provide security for the diplomatic compound, and carry out other duties here. The Taliban say such a force would violate last year’s Doha agreement.

Once Mr. Biden announced in April the withdrawal of all American combat forces from Afghanistan, the military moved quickly to close bases, remove or destroy gear, and pack up the remnants of the nearly 20-year engagement. Although the military had until Sept. 11, Mr. Biden’s chosen exit date, it has moved faster than expected, and U.S. officials anticipated that all but the bare minimum of troops and equipment would be out by the July 4 weekend.

For a time, the White House toyed with the idea of keeping the Bagram Air Field, built by the Soviet Union decades ago, open longer. That would have allowed the U.S. to maintain a secure airfield to conduct strikes against the Taliban, evacuate Afghan interpreters and others who had assisted the U.S. However, that plan was shelved two weeks ago, when Mr. Biden directed that the airfield be shut down as planned.

Write to Gordon Lubold at Gordon.Lubold@wsj.com and Nancy A. Youssef at nancy.youssef@wsj.com