The Islamic State, also known as ISIS or ISIL, had been surrounded by Lebanese and Syrian forces on both sides of the border and made the deal to win the freedom of its fighters in exchange for turning over the bodies of nine Lebanese soldiers taken prisoner in 2014.
Colonel Ryan said the agreement undermined efforts to fight the Islamic State in Syria.
“The coalition, we are not party to this agreement between Lebanon, Hezbollah and ISIS,” he 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 Ryan said that airstrikes against the Islamic State convoy remained a possibility but had not yet taken place because coalition officials were trying to verify whether civilians were in the group.
The Islamic State fighters were believed to be accompanied by family members in 17 buses and 11 ambulances, and at least 25 of them were wounded, according to statements by Hezbollah officials in Lebanon.
“We’ve seen ISIS use protective sites like hospitals and mosques, seen them drive in ambulances,” Colonel Ryan said. “So if we do identify and find ISIS fighters who have weapons — and like I said, we can discriminate between civilians and ISIS fighters — we will strike when we can. If we are able to do so, we will.”
Lebanese officials praised the deal because it rid the country’s borders of Islamic State fighters and assuaged public concern over the fate of the nine missing servicemen, but others in the region were critical. The Iraqi prime minister, Haider al-Abadi, faulted Syria for relocating the Islamic State fighters to its eastern frontier, which is the border with Iraq.
“We fight the terrorists in Iraq,” he said in a speech on Tuesday. “We do not send them to Syria — we kill them in Iraq.”
Mr. Abadi called on the Syrian government to investigate the decision to relocate the Islamic State fighters.
“There should be full cooperation on the elimination of terrorism, not the evacuation of them from one place to the other,” he said.
The Lebanese government took pains to play down the cooperation of Hezbollah fighters with the Syrian Army on the Syrian side of the border, and of those two forces with its own army on the Lebanese side. It insisted that it was merely coincidental that both sides simultaneously began an offensive against the Islamic State over a week ago and that both sides declared a cease-fire in their fights against the militant group at about the same time on Sunday.
Lebanon, which relies on American military aid for its armed forces, does not want to appear to be acting as an ally of the Syrian government. Hezbollah, which dominates Lebanese politics, makes no secret that it sends militias to fight in Syria and maintains a close alliance with Iran.
The American Embassy in Beirut, Lebanon, did not immediately respond to requests for comment on the safe-passage deal.
Fighting in the Raqqa area of Syria, where the American-led coalition and allied Syrian groups are actively battling the Islamic State, has increased in intensity recently. The Syrian Observatory for Human Rights, based in London, reported on Wednesday that 64 combatants had been killed in the past 24 hours, and 150 in the past six days.