UN Secretary-General Ban Ki-moon has accused both the Syrian government and the opposition of large-scale human rights violations, including torturing and reportedly executing prisoners and failing to protect civilians fleeing the war-ravaged country in record numbers.

In an address to the UN General Assembly, Ban demanded that those responsible for violating international humanitarian and human rights laws be held accountable.

The UN chief went before the 193-nation world body to report on the intensifying conflict which he said has taken "a particularly brutal turn." He warned that "the entire region is being engulfed by the complex dynamics of the conflict." Activists say the civil war has claimed between 23,000 and 26,000 lives.

The UN refugee agency said Tuesday that more than 100,000 Syrians fled their country in August, the highest monthly total since the crisis began in March 2011. A total of 234,368 Syrians have fled to neighbouring countries in the past 17 months, the agency said.

Ban said more than 2.5 million people inside Syria need assistance, along with those who have fled to Turkey, Jordan, Lebanon and Iraq. He urged donors to come forward, saying the UN appeal for $180 million is only half-funded.

Civilians bear brunt of violence

The UN chief accused Syrian forces of indiscriminately shelling densely populated areas with heavy weapons, tanks and military aircraft and urged both sides — but especially President Bashar al-Assad's government — to end the fighting.

Ban lamented that civilians are bearing the brunt of the violence, saying even people in bread lines have been attacked.

"Prisoners on both sides are subject to harsh treatment and, often, torture," he said. "There have been alarming reports of summary executions on both sides."

'How many more will be killed and wounded, their lives shattered, before president Assad and his advisers are persuaded to change course?'—Ban Ki-moon

He added, "government forces and the armed opposition have clearly failed to protect civilians and respect the rules of international humanitarian law."

The UN chief urged the world to unite behind a plan to end the conflict.

Missing in all international initiatives so far, Ban said, "is a unity of effort that will have an impact on the ground."

"How many more will be killed and wounded, their lives shattered, before president Assad and his advisers are persuaded to change course?" Ban asked. "How can we convince armed groups that a better future lies not in fighting, but in building the foundations of a new political and social contract that guarantees freedom and justice?"

Syria's most important allies, Russia and China, have vetoed three Western-backed resolutions in the UN Security Council aimed at stepping up pressure on Assad's government to end the conflict by threatening sanctions. As a result, the UN's most powerful body remains paralyzed and unable to address the escalating civil war.

New Syrian envoy

The General Assembly meeting also provided the first opportunity for UN member states to hear from Lakhdar Brahimi, the new UN-Arab League special representative to Syria. Brahimi replaced Kofi Annan on Sept. 1.

U.N. special envoy to Syria Lakhdar Brahimi. U.N. special envoy to Syria Lakhdar Brahimi. (Michel Euler/Associated Press)

Ban urged all countries to unite behind Brahimi's mission, which he called "daunting but not insurmountable."

Ban said Brahimi will visit Cairo shortly for talks with Arab League Secretary-General Nabil Elaraby before heading to Damascus "as soon as possible."

In his brief speech to the General Assembly, Brahimi called the support of the international community for his mission "indispensable and very urgent."

"It will only be effective if all pull in the same direction," he said.