Turkish forces intervened in Syria's civil war to "end the rule of the cruel Assad," President Recep Tayyip Erdogan has said.

Mr Erdogan condemned what he described as the failure of the United Nations in Syria and defended sending tanks, special forces units and fighter jets across the border in August.

"Close to one million people died in Syria, and they continue dying," he said in a speech on Tuesday. "Where is the UN? What are they doing?

"We kept saying 'patience, patience, patience' but could not take it any more and entered Syria."

In pictures: Turkey launches operation in Syria Show all 9 1 /9 In pictures: Turkey launches operation in Syria In pictures: Turkey launches operation in Syria Turkish tanks driving to the Syrian-Turkish border town of Jarabulus yesterday AFP/Getty In pictures: Turkey launches operation in Syria Turkish-backed gather on the outskirts of Jarabulus, Syria, ahead of an offensive on 24 August 2016 Reuters In pictures: Turkey launches operation in Syria Turkish army tanks make their way towards the Syrian border town of Jarabulus, Syria August 24, 2016 Reuters In pictures: Turkey launches operation in Syria Turkish soldiers return from Syria to Turkey with tanks after a military operation at the Syrian border as part of their offensive against the Islamic State (IS) militant group in Syria, Karkamis district of Gaziantep, Turkey, 25 August 2016 EPA In pictures: Turkey launches operation in Syria Turkish army tanks and Turkey-backed Syrian opposition forces move toward the Syrian border as pictured from Karkamis, Turkey, AP In pictures: Turkey launches operation in Syria Turkish tanks on their way to the Turkish-Syria border during an operation against Isis on 24 August 2016 EPA In pictures: Turkey launches operation in Syria Syrian opposition fighters being transported during preparations to enter Jarabulus in Karkamis, Turkey, on 24 August 2016. EPA In pictures: Turkey launches operation in Syria An air strike hitting Isis-controlled territory near Jarabulus, near the Turkish border, on 24 August 2016. EPA In pictures: Turkey launches operation in Syria A Turkish army tank and an armoured vehicle stationed near the border with Syria. Turkish media reports say Turkish artillery has launched new strikes at Isis targets across the border AP

He said Turkey had "no interest in Syrian territory" and added: "We are there to bring justice. We are there to end the rule of the cruel Assad, who has been spreading state terror."

However, rather than engaging soldiers loyal to the Assad regime, Turkey's Operation Euphrates Shield has mainly sought to dislodge Isis from the border between the two countries and prevent the expansion of Syrian Kurdish militias.

Mr Erdogan's speech made no mention of the besieged city of Aleppo, which the UN has warned is experiencing a "descent into hell" as Syrian regime forces backed by Russian air strikes continue their brutal assault.

Aftermath of airstrike in Aleppo

A senior official from one of the Turkmen rebel brigades backed by Turkey told Reuters around 60 per cent of Turkmen fighters pulled out of Aleppo to take part in Euphrates Shield, withdrawing from the front line against regime forces.

He said "perhaps Aleppo could have resisted more" had the rebels not withdrawn, but added they "did not have much of a chance" with their limited weapons against the regime and the Russians, who "have used everything from barrel bombs to warplanes".

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The Kremlin said Mr Erdogan's statement came as a surprise and it expected an explanation from Ankara.

"It is a very serious statement and one which differs from previous ones and with our understanding of the situation," Kremlin spokesman Dmitry Peskov said.

"We hope that our Turkish partners will provide us with some kind of explanation about this."