BEIRUT — Islamic State militants lost their last foothold in a major city and a strategic border crossing Friday, as the Syrian and Iraqi militaries made significant advances, squeezing the militant group into a shrinking patch of territory near the border.
Syrian government forces, supported by intense Russian airstrikes and Iranian-backed militias on the ground, drove the militants from the last few neighborhoods they controlled in the eastern provincial capital of Deir El-Zour, the Syrian army said.
Across the border, the Iraqi army and allied Iranian-backed militias seized control of a crucial border crossing after taking most of the town of Qaim, Iraq, from the Islamic State, according to the Iraqi military chief of staff.
The military advances dealt a severe blow to the militant group, leaving it with fragments of its self-declared caliphate that once extended from the center of Syria to the outskirts of Baghdad.
They also provided yet another indication that President Bashar Assad’s fortunes have rebounded and that, with help from Russian and Iranian allies, the Syrian army can take back territory.
The Islamic State now maintains just a few pockets of western Anbar province in Iraq and somewhat larger patches in Syria, where it controls about a third of the desert province of Deir El-Zour, including a string of small towns and villages, and an oil field.
The developments also set the stage for a battle for the Syrian border town of Bukamal, on the strategic highway from Baghdad to Damascus, and what appears to be the end game for the remaining ISIS territory.
The seizing of Deir El-Zour punctuates the turnaround Assad has managed in more than six years of war. Just two years ago, the idea that the government would manage to take back the city seemed remote.
When the Syrian war broke out in 2011, soldiers were defecting from the Syrian army, and only a fraction of the troops could be counted on for loyalty in the field. But Assad hit hard at rebel-held neighborhoods, pummeling Syrian cities with airstrikes with the support of Iran and its Lebanese ally, Hezbollah.
In 2015, Russia entered the war on Assad’s behalf, carrying out airstrikes against the Islamic State and other insurgent factions. Russia’s backing allowed Assad’s forces to focus on one front at a time.
Once the non-Islamic State insurgents were contained, the progovernment alliance turned its attention to the Islamic State, which it has now mostly routed.
Still, Assad is faced with running a country that is still divided, politically and territorially, where major cities are devastated, the security forces deeply dependent on Russia and Iran, and the economy gutted.
The government’s announcement of victory in Deir El-Zour came just weeks after a US-backed, Kurdish-led militia, called the Syrian Democratic Forces, took over the city of Raqqa, which had served as the de facto capital of the Islamic State.
The militants never controlled the whole of the city of Deir El-Zour, although they held most of the surrounding province, an oil-rich region that provided an important source of revenue to the Islamic State.
For 2½ years, though, the Islamic State had surrounded and besieged 200,000 civilians in the government-held section of the city. Its population dwindled to 90,000, the United Nations estimates, as people escaped or were smuggled out.
Now, the group’s most important territory is the border town of Bukamal and the border crossing on the Syrian side. Iraqi forces claimed the other side of the border Friday, along with most of Qaim, Bukamal’s counterpart on the Iraqi side.
That battle for the remaining Islamic State territory could inflame tensions among the competing forces fighting the militants as they converge on the region: the Russian and Iranian-backed alliance that supports the Syrian government; the rival US-backed SDF, and the Iraqi forces that are pursuing Islamic State holdouts on their side of the border.
The stakes are high, with the competing armies seeking not only to vanquish the Islamic State, but also racing against each other to win influence in the strategic border zone.
The fighting could escalate as the SDF, backed by US warplanes, and the progovernment alliance, which has Russian air support, both advance against the Islamic State’s remaining pockets in Deir El-Zour province.