ISTANBUL (AP) -- The Islamic State group could inadvertently benefit from a situation in which Syrian government forces are considerably weakened on the ground, a London-based military analysis group said on Tuesday.
The report, published by IHS Jane's Terrorism and Insurgency Centre, follows the United States bombing of a Syrian army base after a chemical weapons attack on April 4 killed nearly 90 people.
The U.S. has accused the Syrian government of being behind the attack -- charges that Syria denies.
In Syria, the Islamic State group is battling both government forces and forces allied with the U.S.-led coalition.
If Syrian government forces are weakened, IS fighters could more easily move into heavily populated cities and towns, said Columb Strack, senior Middle East analyst at IHS Markit.
"The Syrian government is essentially the anvil to the U.S.-led coalition's hammer," Strack said.
Weakened Syrian government forces could give the militants additional footholds at a time when their grip on territory elsewhere in Syria and Iraq is being rolled back, Strack explained.
In Iraq, IS has lost more than half the territory the militants once controlled there and is now fighting to defend a cluster of western Mosul neighborhoods that mark the last significant urban area the group holds in that country.
Across both Iraq and Syria, IS has lost nearly half the territory it held at the height of its power in 2014. Since then, a combination of more intense U.S.-led coalition involvement in the fight against IS and Syrian government advances in Aleppo and Palmyra have pushed IS out of more than 40,000 square kilometers (15,400 square miles) of territory.
The U.S.-led coalition and the fighters it backs are moving to surround Raqqa before attacking the northern Syrian city, which is the extremist group's self-declared capital.
Predominantly-Kurdish Syrian Democratic Forces, backed by the coalition, announced they have surrounded the town Tabqa, some 40 kilometers (25 miles) southwest of Raqqa with U.S.-led air and ground support.
However, Strack said while coalition forces are focused on Raqqa, IS may be poised to gain territory in another city -- Deir el-Zour -- if the Syrian government forces holding the militants back there are weakened.
"The capture of Deir el-Zour, the largest city in eastern Syria, could be a life-line for the group's governance project beyond the loss of Mosul and Raqqa," Strack said in the report, adding that the city could serve as "a new major population center from which to run the caliphate."