The bodies were given back to Lebanese forces between Sunday and Tuesday.

Colonel Dillon said the pact undermined efforts to fight the Islamic State in Syria. Iraq, normally an ally of the Syrian government, joined the American military in criticizing the decision to relocate the militants.

“The coalition, we are not party to this agreement between Lebanese Hezbollah and ISIS,” Colonel Dillon said. “Their claim of fighting terrorism rings hollow when they allow known terrorists to transit territory under their control. ISIS is a global threat, and relocating terrorists from one place to another is not a lasting solution.”

Colonel Dillon said airstrikes directly on the Islamic State convoy remained a possibility but as of late Wednesday had not been carried out because coalition officials were trying to verify whether civilians were intermingled in the group.

“We are monitoring these fighters in real time, we will take action where necessary, those would be absolutely lucrative targets,” he said.

“We’ve seen ISIS use protective sites like hospitals and mosques, seen them drive in ambulances,” the colonel said. “So if we do identify and find ISIS fighters who have weapons — we can discriminate between civilians and ISIS fighters — we will strike when we can. If we are able to do so, we will.”

The militants were loaded into 17 buses and 12 ambulances near Arsal, in northeastern Lebanon, on Monday morning, according to Hezbollah officials in Lebanon, and then taken to the Syrian city of Homs, to the north. Some of the buses were emblazoned with the name of a tour company, Happy Journeys.

In Homs on Tuesday, the Islamic State evacuees were transferred to buses and ambulances sent there by the Islamic State, according to the Syrian Observatory for Human Rights, a monitoring group based in London. They then began what would normally be a 10-hour journey to Abu Kamal.