Russia sent paratroopers into Kazakhstan on Thursday to help put down a countrywide uprising after deadly violence spread across the tightly controlled former Soviet state.

Police said they had killed dozens of rioters in the Central Asian country’s main city Almaty. State television said 13 members of the security forces had died, including two found decapitated.

A presidential residence and the mayor’s office in the city were both ablaze, Reuters journalists said. By Thursday afternoon, the city’s airport, seized earlier by protesters, was under firm control of military personnel. Burnt out cars littered the streets.

Earlier on Thursday, several armoured personnel carriers and scores of troops had entered the main square of Almaty, and gunshots could be heard as troops approached the crowd, Reuters correspondents reported from the scene. Later, the square appeared peaceful, with 200-300 protesters still gathered and no troops around.

Unverified video on social media showed troops patrolling Almaty’s foggy streets overnight, firing weapons, as well as widespread looting in the city. Masked protesters, some carrying shields and batons apparently seized from police, marched through billowing tear gas along a tree-lined avenue, to the sound of detonations.

The Internet had been shut down across the country and the full extent of the violence was impossible to confirm. But the unrest was unprecedented for Kazakhstan, ruled firmly since Soviet times by leader Nursultan Nazarbayev, 81, who had held on to the reins despite stepping down three years ago as President.

Nazarbayev’s hand-picked successor, President Kassym-Jomart Tokayev, called in forces from ally Russia overnight as part of a Moscow-led military alliance of ex-Soviet states. He blamed the unrest on foreign-trained terrorists who he said had seized buildings and weapons.

“It is an undermining of the integrity of the state and most importantly it is an attack on our citizens who are asking me... to help them urgently,” he said.

Moscow said it would consult with Kazakhstan and allies on further measures to support the Kazakh authorities’ “counter-terrorist operation” and called the uprising a foreign-inspired attempt to undermine the country's security by force.

Neither Kazakhstan nor Russia provided evidence to support the claim of foreign involvement. The secretariat of the Russian-led Collective Security Treaty Organisation said advanced units of Russian paratroopers were in the country.

Troops being sent included units from Belarus, Armenia, Tajikistan and Kyrgyzstan as well as Russia, the secretariat said. It did not disclose the overall size of the force.

The uprising, which began as protests in the west of the country against a New Year’s Day fuel price hike, had swelled dramatically on Wednesday, when protesters stormed and torched public buildings in Almaty.

They chanted slogans against Nazarbayev, and in at least one case looped ropes around a bronze statue of him.