WASHINGTON (Reuters) - Afghanistan told the United States that Islamic State fighters who surrendered last week will be treated as prisoners of war, and not honored guests, despite the warm welcome they had initially received, a top U.S. general said on Wednesday.

FILE PHOTO - General Joseph L. Votel, Commander of United States Central Command (CENTCOM) speaks during the Change of Command U.S. Naval Forces Central Command 5th Fleet Combined Maritime Forces ceremony at the U.S. Naval Base in Bahrain, May 6, 2018. REUTERS/Hamad I Mohammed

While pressure has been building for peace talks between the Western-backed government in Kabul and the Taliban insurgency, U.S. officials say Islamic State’s branch in Afghanistan is not part of any reconciliation push and instead must be wiped out.

Even by the bloody standards of the Afghan war, Islamic State has gained an unmatched reputation for brutality, routinely beheading opponents or forcing them to sit on explosives.

But last week, an Afghan governor’s office floated the possibility of amnesty for a large group of Islamic State fighters, including two senior commanders, who gave themselves up after being driven from their strongholds by Taliban insurgents.

U.S. Army General Joseph Votel, head of the U.S. military’s Central Command, said the Afghans acknowledged the surrender, the largest of its kind so far by Islamic State, “could have been handled better.”

“The government of Afghanistan has assured us that these ISIS-K fighters will be treated as war prisoners,” Votel told a news briefing at the Pentagon, using an acronym for the Afghan affiliate of the group.

Votel said that the fighters would be investigated and held to account for any war crimes they committed.

Civilians who fled the last clashes have accused Islamic State fighters of atrocities, giving detailed accounts of women and young girls being taken from their families, raped and, in some cases, murdered.

“They have essentially waged a pretty vicious campaign against the people without regard to civilian casualties,” Votel said.

In another example of Islamic State’s tactics, the group on Saturday claimed responsibility for a suicide bombing on a Shi’ite Muslim mosque in eastern Afghanistan that killed 39 people and wounded at least 80 others.

As the U.S.-backed Afghan army presses Afghan insurgents, the central government in Kabul is also pursuing peace with their main enemy, the Taliban, even declaring a three-day ceasefire in June that saw unarmed Taliban fighters mingling with soldiers on the streets.

Perhaps in that context, local Afghan officials had initially hoped that treating this batch of Islamic State fighters well would entice more of them to surrender.

That, however, was not the approach of the United States or of the central government in Kabul, Votel said.

Although Washington ultimately seeks an Afghan-led peace agreement with the Taliban, Votel said the U.S. and Afghan position on Islamic State was clear: “We’ve all agreed (it’s) an organization that just needs to be destroyed.”

The back-and-forth over Islamic State speaks volumes about confusion as Kabul and the West are trying to find a way to end 17 years of war against insurgents.

U.S. President Donald Trump a year ago reluctantly agreed to an open-ended deployment of U.S. military advisers, trainers and special forces and increased air support for Afghan forces. Roughly 14,000 U.S. troops are deployed in Afghanistan along with 8,000 other coalition forces, according to Pentagon data.

But Trump has proven capable of reversing himself and U.S. officials privately acknowledge a sense of urgency to show that America’s longest war can still bring a degree of stability to Afghanistan. A senior U.S. diplomat met with a Taliban representatives in Doha in July.

Votel acknowledged that the incoming U.S. commander, Army General Scott Miller, would do his own review but predicted no major changes to the war plan approved by Trump last year.

“I can’t predict exactly what General Miller may say in terms of this. But as I’ve commented, my personal view is that the strategy we have in place is the right one,” Votel said.