The UN envoy to Syria Lakhdar Brahimi has said Syria's war has reached "unprecedented levels of horror".
He was speaking after almost 80 men were found shot dead and dumped in a river in the battlefront city of Aleppo yesterday.
Brahimi told the divided UN Security Council last night it has to act now to halt the carnage.
Meanwhile, Ireland is preparing to give another €4.7m in aid to help victims of the conflict.
The announcement will be made at a humanitarian-aid pledging conference for Syria chaired by UN Secretary General Ban Ki-moon, where it is hoped funds of up to $1.5bn can be raised.
Minister Costello said the money would go to those most in need.
"The humanitarian need is absolutely dire…We're very careful to make sure the money is spent properly to provide all the humanitarian aid that's required," he said.
Syria Lakhdar Brahimi told the United Nations Syria “is being destroyed bit by bit” and warned his mediation effort could not go forward unless the world body united to push all sides towards a compromise.
The UN Security Council has been divided over Syria for months, with the United States, Britain, France and other Western powers backing the armed opposition and pushing for resolutions that raised the threat of sanctions. Three times, Russia and China have cast vetoes to block those resolutions.
“I’m embarrassed to be repeating the same thing: Syria is being destroyed,” Lakhdar Brahimi said after closed-door consultations with the security council.
Mr Brahimi blamed both Syrian president Bashar Assad’s government and the Western-backed opposition forces.
“Objectively, they are co-operating to destroy Syria. Syria is being destroyed bit by bit. And in destroying Syria, the region is being pushed into a situation that is extremely bad, and extremely important for the entire world,” he said.
He said that was why the security council had a duty to overcome its divisions.
Mr Brahimi suggested that the security council revisit the Geneva Communique of June 2012, a broad but ambiguous proposal endorsed by the Western powers and Russia to provide a basis for negotiations.
Assad’s role in any transition government was a red line during the negotiations of the Geneva Communique, and was left vague. The United States and Russia continue to disagree on Assad’s role, though both signed off on the communiqué.
Mr Brahimi says the security council should now look toward the provisions of the Geneva Communique as a solution.
“A very critical element is the creation of this governing body, which is really a transition government, with full executive powers,” he said.
“I think there was a very clever creative ambiguity in this creation, but I told them that ambiguity has to be lifted now. Now you have to say what those full executive powers would be. All the powers of state have got to go to that government,” he told reporters outside the council.
Without a council push on the Assad government and opposition, the Geneva Communique and his mediation “cannot be implemented as it is”, he said.
Mr Brahimi addressed widespread rumours that he was about to quit, as his predecessor, former UN secretary-general Kofi Annan, did last year when he ran into a similar impasse.
“Am I going to resign? I am not a quitter,” Mr Brahimi said. “The United Nations has no choice but to remain engaged with this problem, whether I am there or not. The moment I feel I am totally useless, I will not stay one minute more.
“So if I’m doing it, it is because, maybe stupidly, I feel a sense of duty.”
The humanitarian situation in Mali is also said to be critical, according to community development organisation Plan Ireland. The body is calling for people to donate what they can to those caught in the crisis.
People are continuing to flee the country as the fighting sweeps across the nation.
The call for aid comes on the day an international donors conference is due to open in Ethiopia to raise $950m to fund the military campaign in Mali.