KABUL, Afghanistan — Army Lt. Gen. James Rainey became one of the most important leaders of NATO’s Resolute Support mission Friday when he assumed command of Combined Security Transition Command-Afghanistan.

The new commander said he was “excited” to be at the helm of CSTC-A, one of the largest commands in Afghanistan, which is tasked with building Afghanistan’s security forces and is responsible for many of the NATO mission’s essential functions.

“I can promise you that every day I am here, you will get 100 percent of what I’ve got,” Rainey told a crowd of about 100 Afghan, NATO coalition and U.S. military and civilian leaders at a ceremony closed to the media. His quotes were released in a statement after the event.

Stars and Stripes reported last week that Rainey would likely take over command from Maj. Gen. Robin Fontes, who held the highest position of any female servicemember in the war that's entering its 18th year. Rainey was promoted from major general during a separate ceremony Thursday.

News of a leadership shakeup surprised many in Kabul’s military and diplomatic communities, as Fontes was expected to remain in her position until next summer. She assumed command in July 2017. Military officials declined to say what’s next for Fontes.

Officials have insisted that the switch — which comes a little more than a month after Gen. Scott Miller took over command of U.S. and NATO forces from Gen. John Nicholson — is a normal rotation of leadership.

“(Maj.) Gen. Fontes has done a fantastic job,” Gen. Joseph Votel, head of U.S. Central Command, said last week. He dismissed suggestions that the reshuffling was part of a new approach to the war after Miller took over.

“I expect that Gen. Miller and the team going forward will continue to approach this with the same vigor that Gen. Nicholson and (Maj.) Gen. Fontes did,” Votel said.

Miller thanked Fontes for her leadership at Friday’s ceremony, before describing CSTC-A as “the central pillar of what we’re trying to do in Afghanistan with our Afghan partners.”

Rainey — who was assigned to the Pentagon in January as assistant deputy chief of staff for the Army, and before that commanded the 3rd Infantry Division, and served as deputy commanding general for U.S. Forces-Afghanistan and commander of Bagram Air Field — returns to Afghanistan as local forces appear far from sustainable or independent of American support.

The Taliban control or contest about 40 percent of Afghanistan’s districts, according to the U.S. military. However, analysts say the number is much higher.

In August, Taliban fighters overran an Afghan base in northern Faryab province after troops ran out of ammunition, food and water despite requesting supplies, an Afghan official told Stars and Stripes.

At the same time, Afghan forces were battling other Taliban fighters who had launched an attack on the strategic city of Ghazni, less than 100 miles from Kabul. Insurgents had pushed deep into the city and U.S. air support was needed to push them back, which resulted in civilian casualties, according to a U.N. report released this week.

Last month, Defense Secretary Jim Mattis said the U.S.-led coalition was adjusting tactics to address mounting casualties among Afghan forces. His comments came a day after the Afghan defense minister said more than 500 Afghan soldiers had been killed in August, a record for a single month.

Before Friday’s ceremony Fontes was awarded the Defense Superior Service Medal, Second Oak Leaf Cluster, for her service as head of CSTC-A.

During her time in charge, the two-star general oversaw the adoption of a new pay system for Afghanistan’s Defense Ministry, the integration of UH-60 Black Hawks into the country’s air force and improved procurement and contracting process.

Corey Dickstein contributed to this report.

wellman.phillip@stripes.com Twitter: @pwwellman

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