The deaths of nearly 70 civilians in a Syrian town reclaimed from Islamic State has been called a "shocking massacre" by an official.

At least 35 people were found dumped in a shaft after they had been shot during three weeks of terror in Qaryartayn.

The number of dead stands at 67 and is expected to rise, with the UK-based Syrian Observatory for Human Rights documenting 128 killings in the last days of IS rule in the town.

Talal Barazi, the governor of Homs province where the discovery was made, says the search continues, with 13 residents still missing, and six bodies unidentified.

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He said most of those killed were government employees, or people associated with Syria's ruling Baath party.

He said the killings went on for the three weeks that IS was in town and "terrorised" its residents.

The head of the Observatory, Rami Abdurrahman, said what happened in the town was a "massacre".

The Observatory also said it documented at least 12 killed at the hands of pro-government troops after they regained control of the town.

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IS militants first seized Qaryatayn in August 2015, and relied on the strategically-located town to defend another of their bastions, the historic city of Palmyra.

At the time, thousands of the town's Christian residents fled, fearing the extremist group's brutality.

With Russian backing, Syrian troops regained control of the town in April 2016.

But IS, facing major setbacks around Syria and Iraq, launched a new attack on the town in late September and recaptured it.

Government forces regained control of Qaryatayn on Saturday.