Suspected US-led coalition air strikes have killed at least 26 civilians in a Syrian village, piling pressure on the alliance after allegations that another bombing raid left regime soldiers dead.

The coalition has been bombarding the Islamic State group for more than a year in Syria and neighbouring Iraq, where the jihadists have declared a self-styled caliphate.

But according to a monitoring group, strikes yesterday on the village of Al-Khan in northeastern Syria only left civilians dead.

Rami Abdel Rahman of the Syrian Observatory for Human Rights said IS is in control of Al-Khan but is only on its outskirts, "which is why all of the deaths were civilians".

The death toll included at least seven children and four women, he said, adding that it was likely to rise as more than a dozen civilians were still missing under rubble.

A spokesman for the US-led coalition said he had no details yet about the raid, but that a "credibility assessment" would review claims of civilian deaths.

Last month, the US said four civilians were "likely" to have been killed in strikes against IS in Iraq. And in November 2014, it admitted accidentally killing two children in a strike in Syria.

The Al-Khan strike came with the coalition already under pressure over allegations it carried out a raid the previous day that killed Syrian soldiers, in the first such case.

In a letter to the UN Security Council and Secretary General Ban Ki-moon, Syria accused the coalition of targeting an army camp in the eastern province of Deir Ezzor on Sunday, killing three soldiers and wounding 13.

The foreign ministry letter condemned the attack as "a flagrant aggression".

The Observatory said four soldiers died in the first incident of US-led strikes killing Syrian troops.

A Syrian military source gave the same toll, and said the attack late Sunday hit several buildings used as weapons depots and an army training camp, damaging two tanks.

But a coalition spokesman said its only strikes in the area on Sunday were on an oil wellhead some 55 kilometres southeast of the army base, and a US official, speaking on condition of anonymity, blamed Russian strikes for the deaths.

Much of Deir Ezzor is under IS control, but the regime still has a presence in small areas, including in the provincial capital.