ALEPPO (AFP) - Car bombs tore Wednesday through Syria’s second city Aleppo, leaving dozens dead, as shells from the conflict crashed into neighbouring Turkey, killing five and prompting an angry Ankara to contact the UN.

Two blasts went off in quick succession near a military officers’ club around Aleppo’s Saadallah al-Jabiri Square, ripping off a hotel’s facade and flattening a two-storey cafe, an AFP correspondent reported.

A third exploded soon after at an entrance to the Old City in Bab Jnein, the Syrian Observatory for Human Rights and a military official said.

A man whose family owns a coffee shop overlooking the square described the sound of the blasts as “terrifying”.

The Observatory said at least 50 people were killed and almost 100 wounded, adding “most of them were regime troops”. An official said 37 people died.

“We heard two enormous explosions, as though the gates of hell were opening,” Hassan, an employee of a nearby hotel, told AFP.

“I saw thick smoke, and I helped a woman on the pavement whose arms and legs were completely dislocated,” said Hassan.

The bloodshed spilled into neighbouring Turkey when shells hit the border town of Akcakale.

“Five people, including a mother and her three children, were killed,” said Abdulhakim Ayhan, mayor of Akcakale, where the shells exploded after being fired from Tall al-Abyad on the Syria side.

It was the second time that fire from Syria has killed people inside Turkey since the uprising against President Bashar al-Assad’s regime erupted in March 2011. Turkey’s deputy prime minister Besir Atalay said the incident “is very serious and goes too far.”

US Secretary of State Hillary Clinton said Washington was “outraged” by the shelling into Turkey, while the Nato military alliance, of which Ankara is a member, strongly condemned it.

Turkish Foreign Minister Ahmet Davutoglu contacted UN chief Ban Ki-moon and UN-Arab League peace envoy Lakhdar Brahimi, his office said, adding the minister chaired an emergency meeting to deal with the incident.

Davutoglu told Ban of “his government’s deepest concern at the incident today in Turkey where a shell apparently emanating from Syria killed a number of civilians,” the UN said.

Ban encouraged Davutoglu to “keep open all channels of communication with the Syrian authorities with a view to lessening any tension that could build up as a result of the incident,” a spokesman said.

After destroying two tanks overnight, rebels attacked a political intelligence branch in Aleppo as well as a market where a large number of troops were posted, said the Observatory.

“The rebels are now attacking regime troops in the heart of the city,” its director Abdel Rahman told AFP.

“This is part of the decisive battle, and the regime can no longer claim to control the city,” he added.

Aleppo, with a population of 1.7 million people, has been one of the focal points of the conflict since mid-July, when the army promised the “mother of all battles” to clear the city of rebels.

Bombings have increasingly become part of the unrest ravaging Syria, which began in March 2011 as peaceful protests for reform but has since escalated into an armed insurgency, with more than 31,000 people killed, according to activists.

Nationwide, violence killed 147 people on Wednesday, said the Observatory.

Peace envoy Brahimi is due back in the region this week to try to revive talks aimed at ending the bloodshed, although the UN says it is still unclear if he will be able to enter Syria.