This marks the beginning of what appears to be a series of more substantial strikes against Iranian-backed militias, who have been implicated in attacks on US troops in the region.
At least 45 Islamic State militants were killed in the Syrian city of al-Raqqa, a UK-based war monitor reported on Tuesday.
The Syrian Observatory for Human Rights (SOHR) said that most of the militants were killed in airstrikes carried out by the US-led international coalition, reports Efe news.
The international coalition backs the Syrian Democratic Forces (SDF), a Kurdish-led alliance that has been fighting against the IS since 6 June in al-Raqqa, the terror organisation's main stronghold in Syria since it established its self-proclaimed caliphate in 2014.
The SOHR said there were clashes between SDF fighters and IS militants in the neighbourhoods of al-Barid and al-Batani, in the western and eastern parts of the city, respectively.