WASHINGTON/KABUL (Reuters) - A three-star general who leads the Joint Special Operations Command overseeing some of the most sensitive U.S. commando missions has been picked to lead the nearly 17-year-old Afghan war, five U.S. officials told Reuters.

Army Lieutenant General Scott Miller would replace Army General John “Mick” Nicholson, who after more than two years has become the longest-serving U.S. commander of international forces battling the Taliban insurgency.

Nicholson was expected serve through most if not all of the summer months that historically have brought some of the heaviest fighting in Afghanistan, two of the officials said, speaking on condition of anonymity.

The Pentagon declined to comment on Nicholson’s successor.

“We have no announcement on any changes,” said Pentagon spokesman Lieutenant Colonel Kone Faulkner.

One U.S. official familiar with Miller said his past service showed a focused on addressing global militant networks that fuel insurgencies, which could be valuable in the fight against Islamic State in Afghanistan.

The change in command would come at a particularly sensitive time in the Afghan war, in which commanders are under pressure to show progress against a resilient Taliban insurgency. Critics warn that the U.S.-backed Afghan military cannot promise to defeat the Taliban anytime soon or overcome Afghanistan’s vast political divisions and entrenched corruption.

The United States also has been unable to address safe-havens it says the Taliban enjoy in neighboring Pakistan.

U.S. President Donald Trump had long identified with war-weary Americans skeptical about the Afghan war, even advocating withdrawal. But faced with the risks posed by the Taliban, he reversed himself and last August approved the more aggressive strategy that Nicholson has led, with mixed results.

A U.S. government watchdog report released on Monday said there had been few signs of significant progress by Afghan security forces between January and March, despite assertions by the U.S. military that Taliban militants were weakened.

Nicholson, who leads U.S. and international forces in Afghanistan, said in November the country had “turned the corner.”

More than 2,400 U.S. forces have died in the war.