BEIRUT -- Backed by Russian and Iranian firepower, Syrian President Bashar Assad's forces reached besieged troops Tuesday at a garrison in the eastern city of Deir el-Zour, breaking a nearly three-year blockade by Islamic State militants and marking a significant advance against the group.
Re-entering Deir el-Zour would take the Syrian forces and their allied Iranian-backed militias a step closer to controlling the oil-rich eastern province and its capital bordering Iraq. Such a move also would boost Tehran's growing influence in the area.
Assad congratulated his troops on breaking the siege as a "resounding victory" against extremism and vowed to forge ahead until "the last inch" of Syrian territory is liberated. Russian President Vladimir Putin, whose military had fired cruise missiles at Islamic State targets near the city, called it a "strategically important victory over terrorists."
Assad's critics called it an alarming development.
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"It opens the whole province for Iran and its agents there," said Mozahem al-Salloum, an opposition activist from the city who has been in exile since 2013.
Iranian- and Lebanese-backed militias form the core of the pro-Assad forces advancing on Deir el-Zour, he noted.
Iran has been seeking to secure a land corridor from its territory, through Iraq, to the Mediterranean to give it unhindered access to its allies in Damascus and Beirut. Control of Deir el-Zour is a boost for that plan.
By nightfall, activists said, the Islamic State militants had counterattacked with four suicide assaults near where the Syrian troops had linked up.
The advance by the Syrian troops was celebrated as a possible relief for the tens of thousands of civilians trapped in the four government-controlled neighborhoods that have been surrounded by the extremists since early 2015. The Syrian government estimates about 70,000 people have survived on sporadic airdrops of food and supplies during the siege.
Activists noted, however, that the new access road could not yet be used for delivering humanitarian assistance because it was still under attack from the Islamic State.
Deir el-Zour, Syria's largest eastern city, has been divided into government- and Islamic State-controlled parts since 2015. The province is held by the extremists and is where they are expected to fight their last battles. They have lost other major cities, including the Iraqi cities of Mosul and Tal Afar. U.S.-backed Syrian troops are bearing down on Raqqa, the group's self-proclaimed capital that is northwest of Deir el-Zour.
It could take weeks, if not months, for Assad's forces to retake Deir el-Zour from the militant group, which controls about 60 percent of the city's neighborhoods.
Government troops have been advancing on the Euphrates River Valley city for weeks, carrying out a multipronged offensive from the northwest, west and southwest. They took control of a strategic mountain to the northwest of the city last week.
This enabled Tuesday's advance, when pro-government forces reached a military base of the 137th Brigade on the outskirts that has been surrounded for months.
The Russian Defense Ministry said one of its frigates in the Mediterranean unleashed cruise missiles early Tuesday toward Islamic State targets near the city. They fired at a fortified area around al-Shola, where most of the militants are believed to be from Russia and former Soviet republics.
The Defense Ministry said drone footage showed that the missiles destroyed a communications center, command centers, ammunition depots and a repair shop for armored vehicles, as well as killing an unspecified number of fighters. But the militants still control al-Shola, said Rami Abdurrahman, the head of the Syrian Observatory for Human Rights.
The Syrian army command said reaching Deir el-Zour marks "a strategic turn in the war against terrorism" and that the city will be used "to expand military operations in the region."
Information for this article was contributed by Bassem Mroue, Nataliya Vasilyeva and Albert Aji of The Associated Press.
A Section on 09/06/2017