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 focussed 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.