"At least 1,922 fighters from IS, mostly foreigners, have been killed since September 23, 2014 in raids and aerial attacks by the international coalition on IS positions and oil refineries" throughout Syria, the Syrian Observatory for Human Rights said.
The strikes targeted IS positions in the central province of Homs, as well as Aleppo in the north, Hasakeh in the northeast, and Deir Ezzor to the east.
They also struck the northern province of Raqa, where the provincial capital of the same name has become the centre of IS's self-styled "caliphate".
The toll also included 90 fighters from IS's jihadist rival and Al-Qaeda Syrian affiliate Al-Nusra Front, most of whom were killed in coalition strikes on their strongholds in northern Syria. It also included one Islamist rebel who was being held by IS.
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At least 66 civilians, including 10 children, have been killed in the campaign, the Britain-based Observatory said.
The coalition air strikes have provided significant support to Kurdish forces, helping them to expel IS jihadists from the flashpoint town of Kobane on the Syrian-Turkish border in January.
Syria's conflict began with peaceful protests in March 2011, but devolved into a civil war after a bloody crackdown by the government.
The war became even more complex in 2014 with the rise of jihadists, particularly IS, which controls swathes of territory in northern and eastern Syria.
More than 220,000 people have been killed and at least 11.2 million displaced since the beginning of the war.