IS has controlled eastern city for nearly three years

BEIRUT — Backed by Russian and Iranian firepower, President Bashar Assad’s forces reached besieged troops Tuesday at a garrison in Syria’s eastern city of Deir el-zour, breaking a nearly three-year blockade by Islamic State militants.

Re-entering Deir el-zour would bring the Syrian forces and their allied Iranian-backed militias a step closer to controlling the oil-rich eastern province and its capital bordering Iraq.

Assad congratulated his troops on breaking the siege 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 IS targets near the city, called it a “strategically important victory over terrorists.”

Assad critics called it an alarming development.

“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 major boost for that plan.

By nightfall, activists said the IS 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 2015. The Syrian government estimates about 70,000 people have survived on erratic air drops of food and supplies during the siege, which was a major embarrassment to Assad.

Activists noted, however, that the new access road could not yet be used for delivering humanitarian assistance because it was still under attack from IS.

It could take weeks, if not months, for Assad’s forces to retake Deir elzour from the militant group, which controls about 60 percent of its neighborhoods.