A new alliance of rebel groups has started to retreat from the border town after suffering heavy casualties. Anti-IS forces have stepped up operations to uproot the militant group in Iraq and Syria.
US-backed Syrian rebels advanced on the eastern Syrian border town of al-Bukamal, which is held by the self-declared "Islamic State" (IS) militant group.
The New Syrian Army (NSA), an alliance of rebel groups battling IS in Syria, launched the offensive on Tuesday under the cover of airstrikes conducted by the US-led anti-IS coalition.
By Wednesday morning, NSA fighters gained control of a small military base near al-Bukamal after wrestling it from IS militants.
The group was supported by extensive air support from the US-led coalition. Airborne fighters had been dropped on the southern edge of the border town during the offensive, said NSA spokesman Mozahem al-Saloum.
However, the militant group pushed back the rebels, with al-Saloum saying the NSA were unable to keep the base and other outposts.
The operation aimed to sever the militant group's cross-border supply line through the al-Bukamal crossing, which links areas of eastern Syria and Iraq's Anbar province, which is under IS control.
In 2014, the militant group shocked the world when it took control of large swathes of territory in Syria and Iraq, including the latter's third-largest city, Mosul.
Iraqi Lt. Gen. Abdul-Wahad al-Saadi on Sunday announced that the country's troop cleared out the last pocket of IS resistance in the strategic city of Fallujah, saying it had been "fully liberated."