A convoy of Islamic State fighters and their families begins to depart from a besieged enclave on the Lebanese-Syrian border. (Omar Sanadiki/Reuters)

U.S. warplanes on Wednesday blocked a convoy of hundreds of Islamic State fighters who were heading to eastern Syria under the terms of a widely criticized deal brokered by Lebanon’s Hezbollah movement.

The 310 fighters were traveling to the Iraq-Syria border in a convoy of buses after Hezbollah and the Syrian government permitted them to withdraw from a besieged enclave on the Lebanon-Syria border.

The deal triggered a rare outburst of public anger against Hezbollah even among some of its closest allies, notably in Iraq, which is gearing up for an offensive to reclaim Iraqi territory adjoining the area to which the fighters were relocating.

Negotiated withdrawals have been a common tactic in Syria’s six-year-old war and have enabled the Syrian government to reassert its authority over many of the areas that fell to opposition control.

But this was the first publicly announced instance of a deal involving the Islamic State on any battle front in Syria or Iraq since the war against the group geared up three years ago.

The criticisms laid bare a widening rift between the U.S.-led coalition battling the Islamic State and the rival coalition fighting the extremists that includes the Shiite Hezbollah movement, Syria and the Iranian-backed Shiite militias in Iraq.

On Wednesday morning, the U.S.-led coalition moved to prevent the convoy from reaching its destination, cratering the road and blowing up a bridge leading to the Islamic State-controlled town of Bukamal on the Syrian border with Iraq, according to a U.S. military spokesman, Col. Ryan Dillon.

The strikes took place in the vicinity of a desert town called Hamaymah, and although front lines are fluid in that part of Syria, it is the U.S. military’s understanding that the convoy is stuck in Syrian government-held territory, Dillon said.

“ISIS is a global threat, and to relocate terrorists from one place to another for someone else to deal with is not acceptable to the coalition,” he said, using an alternative acronym for the Islamic State. “Our goal is to prevent this convoy from moving to ISIS-held territory to reinforce ISIS elements there.”

The airstrikes did not target the convoy itself because about 300 relatives are also traveling with the Islamic State fighters, he added. A U.S. military statement subsequently said airstrikes targeted a number of individual vehicles and fighters that were “clearly identified as ISIS.”

The strikes and the criticisms triggered a defensive response from Hezbollah leader Hassan Nasrallah, who had called the deal a “great victory” in a televised speech on Monday.

“The number of those transferred was not big: 310 tired, broken, militants who had surrendered and lost the willpower to fight will not change the course of the battle in Deir al-Zour, where there are tens of thousands of fighters,” Nasrallah said in a statement on Wednesday, referring to the province where the Islamic State fighters were headed. He pointed out that the fighters were being transferred from one border region of Syria to another, not to Iraq.

But the planned relocation of the fighters to a town right on the Iraqi border, where they would have easily been able to reinforce militants in Iraq, infuriated many Iraqis. In addition to sending thousands of fighters to help Syrian President Bashar al-Assad, Hezbollah has provided training and advice to some of the Iranian-backed Shiite militias fighting the Islamic State in Iraq, and it is regarded by many as an Iraqi ally.

The anger erupted after photographs showing the armed Islamic State fighters traveling across Syria in air-conditioned buses — one of them marked with the words “Happy Journey” — began circulating on social media. One commentator called the deal “selfish.” Another described it as a “betrayal” of Iraq’s alliance with Hezbollah, Syria and Lebanon.

Addressing a news conference on Tuesday night, Iraqi Prime Minister Haider al-Abadi called for a public inquiry into how the deal came about.

“We are fighting terrorists in Iraq, not kicking them out to Syria,” he said at a news conference on Tuesday. “They are terrorists: Why would one negotiate with them in the first place?”

The leader of one of the Hezbollah-allied Iraqi militias refuted the criticisms. Hadi al-Amiri, who heads the Badr Organization, said that negotiating with the Islamic State could save lives and that he wished there had been a similar deal to avert the high death toll in the battle for the Iraqi city of Mosul.

“Personally, if I could have negotiated with them in western Mosul, I would have,” he said in an interview in Mosul. “It’s better than putting our soldiers and civilians in harm’s way and destroying the city.”

Under the arrangement negotiated over the weekend, the fighters and their relatives were allowed to leave a remote mountainous area spanning the Syria-Lebanon border for the desert town of Bukamal on the Iraqi border. In return, Hezbollah secured the bodies of nine captured Lebanese soldiers who had been kidnapped by the Islamic State in 2014, the bodies of three Hezbollah fighters and the body of an Iranian military adviser who had been decapitated by the Islamic State during a battle on the Iraqi-Syrian border earlier this month.

El-Ghobashy reported from Mosul. Mustafa Salim, also in Mosul, and Suzan Haidamous in Washington contributed to this report.