Isis militants in Raqqa
Isis militants retain a base in Raqqa, Syria Reuters

Air strikes carried out by the US-led coalition against Islamic State (Isis) militants in Syria have killed more than 1,600 people over the past five months, according to a watchdog.

The UK-based Syrian Observatory for Human Rights said almost all of those killed were jihadists aligned with IS or Jabhat al-Nusra.

The monitor recorded a total of 62 civilian deaths as a result of the aerial bombing campaign.

A total of 1,465 members of the Islamic State had been killed in Syria, the majority of whom were foreign fighters, the watchdog said.

The US and a coalition of Arab states launched a bombing campaign against the militants in September 2014, building on its operations against the group in Iraqi territory.

Air strikes have often targeted depots of military vehicles, training facilities and operatives themselves.

Since IS shocked the world in 2014 when it declared the establishment of a caliphate spanning territory in Syria and Iraq, the group's advance has been slowed.

The group suffered a high-profile defeat in the city of Kobani in January, where American air strikes supported a ground operation carried out by Kurdish peshmerga forces.

The jihadists lost 2,000 fighters in that battle alone, the Observatory reported.

Meanwhile, IS lost a battle with Syrian government forces at an airbase and in several villages throughout Deir al-Zor and Hasaka provinces.

However, the militants are a long way from suffering an outright defeat. The group retains a strong presence on the ground and its rule is uncontested across large parts of eastern Syria.

Moreover, it has sought to expand its reach internationally.

An offshoot of the group recently carried out a series of attacks in Libya.

Militants claiming loyalty to IS said they were behind a bomb attack on the residence of the Iranian ambassador in the capital city of Tripoli on 22 February.

Earlier in February, militants loyal to IS carried out suicide bombings and executed a group of Egyptian Coptic Christians.