Blast brought down six-storey building in the Syrian rebel-held town of Sarmada, close to the Turkish border.

An explosion flattened a residential building in Syria‘s war-torn northwest, killing at least 36 people including 12 children.

The blast brought down the six-storey building in the town of Sarmada, 350km north of the capital Damascus, close to the Turkish border.

The White Helmets rescue group, also known as the Syrian Civil Defence, described the scene on Sunday as one of “destruction and death,” adding 10 people had been rescued from under the rubble.

The group said the cause of the blast was unknown.

With no end to the carnage in sight, 36 dead civilians and dozens of wounded are the current count of victims of the massive explosion in #Sarmada city at dawn today. #WhiteHelmets are working tirelessly, searching and rescuing, in unbelievable areas of destruction and death. pic.twitter.com/fr1bZGq3O1 — The White Helmets (@SyriaCivilDef) August 12, 2018

The Syrian Observatory for Human Rights, a UK-based war monitor, said the building was believed to be storing weapons and ammunition. It said civilians displaced during the country’s seven-year war also resided there.

In recent weeks, the Syrian government and its main ally Russia have stepped up an offensive to defeat rebels holding territory in Syria, capturing a string of villages straddling the southern provinces of Deraa and Quneitra, as they edge closer to a 1974 demilitarised zone with Israel .

Backed by Russian air power, Syrian government forces have been able to seize control of most of southwestern Deraa province, including the provincial capital of the same name.

Deraa city was the cradle of the uprising against President Bashar al-Assad more than seven years ago.

The government is currently fighting rebels in Idlib, the opposition’s last major stronghold in the country.

Idlib province – with an estimated two million people, including thousands of internally displaced from other parts of Syria – was part of a de-escalation deal signed by Iran, Russia and Turkey, which calls for the cessation of hostilities between rebels and government forces.

The Syrian civil war started as a largely peaceful protest against Assad in March 2011, but quickly developed into a full-scale war after the Syrian leader refused to concede power.

UN special envoy to Syria, Staffan de Mistura, has estimated at least 400,000 people died over the first five years of conflict.