The Syrian military announced Friday that its forces recaptured the eastern city of Dair Alzour, Islamic State's last major urban stronghold in the country, as their Iraqi counterparts wrested control of a key border town from the extremist group.
The simultaneous assaults have squeezed the militants, who once controlled vast stretches of Syria and Iraq, into a dwindling pocket of territory straddling the border between the two countries.
Syrian state media reports said government troops, backed by Russian warplanes and Iranian-supported militias, drove the militants from their remaining footholds in Dair Alzour and were "sweeping" the city to remove any explosive devices left behind.
Hours later, Iraqi Prime Minister Haider Abadi said his forces had taken control of the town of Qaim after seizing a key border post. In a statement issued by his office, Abadi congratulated the country's military, federal police and allied militias for the operation launched just over a week ago, which he said was completed in "record time."
The advances marked the latest in a string of military defeats for Islamic State, which has seen its self-declared caliphate crumble in the face of multiple offensives in Syria and Iraq.
A U.S.-backed alliance of Syrian militias took control of Islamic State's de facto capital, Raqqah, last month, and Iraqi forces recaptured Mosul, the largest city held by the militants, in July.
But as Islamic State loses territory, concern is mounting that the myriad forces arrayed against the militants could turn on each other. Clashes have already erupted in Iraq as Abadi's troops have moved into contested areas that had been under the control of Kurdish fighters known as the peshmerga.
Syrian officials say they are determined to take back all territory that has fallen from government control since the start of an uprising in March 2011. They may soon focus their attention on oil fields seized by the U.S.- backed fighters known as the Syrian Democratic Forces, an alliance of Kurdish and Arab militias, in a race for control over Islamic State's remaining territory in Dair Alzour province.
Lelwa Abdullah, a spokeswoman for the Syrian Democratic Forces, accused the government of shelling their positions at the Jafra oil field over the weekend. The Kurdish-led troops have also been contending with periodic attacks by suicide car and truck bombers unleashed by Islamic State, she said.
The city of Dair Alzour, which sits on the west bank of the Euphrates River, was considered a key asset by Islamic State because of its proximity to the Iraqi border and to oil and gas fields that were an important source of revenue for the militants.
Assad's forces and their allies punched their way into the city in September, breaking a nearly three-year siege on the handful of neighborhoods that had remained under government control since the militants' lightning sweep across Syria and Iraq in 2014.
Brig. Gen. Ali Mayhoub, a Syrian military spokesman, described the city's recapture Friday as a strategic victory, citing its economic importance as well as its location at a crossroads linking the country's eastern, northern and central regions.
"The liberation of Dair Alzour constitutes the final phase in the complete elimination of the Daesh organization in Syria," he said in a statement read on state television, using an Arabic acronym for the militants.
Pro-government forces and their U.S.-backed rivals are now charging south toward the border town of Bukamal, the last urban area under the full control of Islamic State, from opposite sides of the Euphrates river as Iraqi forces close in from the east.
The fighting has displaced tens of thousands of civilians, who have poured into overcrowded camps where food and medicine are in short supply and there aren't enough tents to go around.
Many will be eager to return to Dair Alzour and surrounding villages, although it is not clear how many have a home still standing.
The area has been pounded with artillery and air strikes for months. Video posted on the website of the official Syrian Arab News Agency showed government troops rolling through a devastated cityscape, past collapsed buildings and ones with their facades blown off. Plumes of smoke rose from the skyline.
Resol is a special correspondent.
2:40 p.m.: This article was updated with comment from the Syrian military and the rival Syrian Democratic Forces.
8:30 a.m.: This article was updated throughout with Times staff reporting.