BEIRUT — More than 2,000 Syrians — almost half of them progovernment forces — have been killed in just over two weeks of fighting in Syria, marking one of the worst death tolls in the country’s three-year civil war, opposition activists said Monday.
The reports reflect a recent surge in deadly attacks by the Al Qaeda-breakaway Islamic State group targeting President Bashar Assad’s forces, signaling shifting priorities as Sunni militants seek to consolidate their hold on territory and resources in northern Syria.
Assad’s forces have gained momentum in the fighting with rebels seeking to topple him from power. Infighting also has hurt the rebel cause, with Islamic extremists battling more moderate fighters who have been greatly weakened by lack of weapons and clashes with the militants.
But a series of recent setbacks for the Syrian government at the hands of the Islamic State group threatens to overturn government successes, pitting the Syrian army against a formidable force that now controls large chunks of territory in the country’s north and neighboring Iraq.
‘‘Now that they’ve mopped up rebel resistance to them in the east, the Islamic State [group] can turn to the regime,’’ said Aymenn al-Tamimi, an expert on militant factions in Syria and Iraq. ‘‘It may have been a benefit [to the Islamic State] to deal with rebels first, but the assault against the regime was inevitable.’’
The recent attacks came after Assad was reelected last month to a third seven-year term in a vote that was confined to government-controlled areas and dismissed by the opposition and its Western allies.
In his inauguration speech on July 16, he confidently declared victory and praised his supporters for ‘‘defeating the dirty war.’’
Since then, fighters from the Islamic State group have launched attacks against army positions in three different provinces in northern and central Syria. In the past week alone, the militants struck in three provinces, capturing a government-controlled gas field and two major army bases.
More than 300 soldiers, guards, and workers at the Shaer field were reported killed by Islamic State militants in a three-day offensive. The army recaptured Shaer this past weekend.
Militants last week also overran the sprawling Division 17 military base in the northern Raqqa province, killing at least 85 soldiers inside. Amateur videos posted online by activists showed more than a dozen beheaded bodies in a busy square said to be in Raqqa.
On Sunday, the militants seized the army’s Regiment 121 at Maylabieh in the northern Hassakeh province after a three-day battle.
Beyond Syria, the Islamic State fighters have seized large swaths of land in northern and western Iraq and have declared a self-styled caliphate across territory straddling the Iraq-Syria border.
The Britain-based Syrian Observatory for Human Rights said more than 2,000 people have been killed since Assad’s inauguration, nearly half of them soldiers and government-allied militiamen.