BEIRUT — 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 Iraqi-Syrian border in a convoy of buses after Hezbollah and the Syrian government permitted them to withdraw from a besieged enclave on the Lebanese-Syrian 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.