Syrian soldiers killed in suspected US airstrike

Four Syrian soldiers were killed and 13 injured when a bombing raid by the US-led coalition hit an army camp in the east of the country, a monitor said on Monday.

The Britain-based Syrian Observatory for Human Rights said an air raid "by the international coalition" hit the camp in the west of Deir Az-Zour province, "around two kilometres (one mile) from an area controlled by the Islamic State group".

The Observatory said it was the first time that a strike from the US-led coalition had killed Syrian government troops.

"Regime forces have never previously been hit by raids from the international coalition, which was targeting extremist bases and oil tankers in Deir Az-Zour," Observatory director Rami Abdel Rahman said.

Syria's foreign ministry on Monday condemned the airstrikes as a "flagrant aggression".

"The Syrian Arab Republic strongly condemns this flagrant aggression by the US-led coalition forces, which blatantly violates the objectives of the UN charter," the foreign ministry said in a letter to the UN Security Council and secretary general.

"The Syrian foreign ministry demands the UN Security Council act immediately in the face of this aggression and take appropriate measures to prevent its recurrence," the letter added.

However, the US-led coalition fighting the Islamic State group denied on Monday that its planes had carried out the airstrikes.

"We've seen those Syrian reports but we did not conduct any strikes in that part of Deir Az-Zour yesterday. So we see no evidence," said Colonel Steve Warren, spokesman for the coalition.

He said the coalition's only strikes in Deir Az-Zour on Sunday were some 55 kilometres (34 miles) away from the area where the troops were allegedly killed.

The New York Times reported that a senior US official blamed the Russians for what he described as the "screw-up".

"We've got a radar track showing a Backfire bomber flying directly over the town that the Syrians named a few minutes before the first claims that we killed some Syrian troops," said the official who was quoted by the paper on the condition of anonymity.

The US-led coalition has been targeting IS in Syria since September last year, expanding a campaign that began with raids in neighbouring Iraq.

Its operations have expanded further in recent days.

Syria's conflict has taken the lives of more than 250,000 people, and another four million have been forced to flee the country since it erupted in March 2011.