Syria expressed outrage on Monday after a suspected US-led coalition strike killed ­government troops, though the coalition has denied that its warplanes hit an army base.

In a letter to the UN Security Council and Secretary-General Ban Ki-moon, Syria's foreign ministry condemned what it called an act of "flagrant aggression" that killed at least three soldiers late on Sunday.

"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 the letter.

"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.

The foreign ministry's complaint said three Syrian soldiers were killed and 13 wounded in strikes by four coalition planes on an army camp in the eastern province of Deir Ezzor.

But a spokesperson for the US-led coalition said its only strikes in the area on Sunday were some 55 kilometers southeast of the Syrian army base.

A Syrian military source and the Syrian Observatory for Human Rights, a Britain-based monitor, said four soldiers had been killed and 13 injured in the strike, near the town of Ayyash.

The military source said on condition of anonymity that the attack happened on Sunday night and also damaged two tanks at the military base.

He said the strikes hit an army training camp and several buildings used as weapons ­depots.

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

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

The US-led coalition regularly targets Islamic State (IS) group fighters and installments in the province of Deir Ezzor, much of which is controlled by the militant group, but the Syrian government remains present in small areas, including in the provincial capital.

The coalition began airstrikes in Syria in September 2014, expanding a campaign against IS that began in neighboring Iraq.

Colonel Steve Warren, spokesperson for the coalition, denied that US-led forces were behind the alleged strikes.

"We've seen those Syrian reports, but we did not conduct any strikes in that part of Deir Ezzor yesterday. So we see no evidence," he said.

"We struck 55 kilometers away from the area that the ­Syrians say was struck. That was the only area in Deir Ezzor we struck yesterday," he added.

"There were no human ­beings in the area that we struck yesterday, all we struck was a wellhead."

Brett McGurk, President Barack Obama's special envoy to the coalition, also dismissed the claims on Twitter, saying that "reports of coalition involvement are false."