Observers from the UN Supervision Mission in Syria (UNSMIS) confirmed the horrific killings after having viewed the bodies in the village of Houla. They also confirmed from an examination of ordnance that artillery and tank shells were fired at a residential neighbourhood.
"This appalling and brutal crime involving indiscriminate and disproportionate use of force is a flagrant violation of international law and of the commitments of the Syrian government to cease the use of heavy weapons in population centres and violence in all its form," said a statement issued on behalf of UN Secretary-General Ban Ki-moon and the Joint Special Envoy of the UN and the League of Arab States for Syria, Kofi Annan.
"Those responsible for perpetrating this crime must be held to account," it added.
The Secretary-General and the Joint Special Envoy extended their profound sympathies to the families of the victims and to the wounded, underscoring their grave concern about the lack of protection for civilians in Syria.
General Robert Mood, the head of UNSMIS, issued a statement in which he said that UN observers went to Houla, where they counted more than 32 children under the age of 10 and over 60 adults killed.
"The circumstances that led to these tragic killings are still unclear," the statement noted, while adding that whoever is responsible for this "deplorable act of violence" should be held accountable.
"This indiscriminate and disproportionate use of force is unacceptable and unforgivable. The killing of innocent children and civilians needs to stop," the statement by Mood said.
Ban, Annan and Mood strongly demanded that the Syrian Government immediately cease the use of heavy weapons in population centres, and called on all parties to halt violence in all its forms.
Annan is contacting the Syrian authorities to convey the expectations of the international community, and he will also do so during his forthcoming visit to Syria.
The UN estimates that more than 9,000 people, mostly civilians, have been killed in Syria and tens of thousands displaced since the uprising against President Bashar al-Assad began some 14 months ago.
The violence prompted the UN Security Council to establish UNSMIS, with up to 300 unarmed military observers, to monitor the cessation of violence and support the full implementation of the six-point plan put forward by Annan.
The peace plan by Annan calls for an end to violence, access for humanitarian agencies to provide relief to those in need, the release of detainees, the start of inclusive political dialogue that takes into account the aspirations of Syrian people, and unrestricted access to the country for the international media.
US Secretary of State Hillary Clinton also condemned "in the strongest possible terms" the massacre in the Syrian village of Houla which left hundreds wounded.
The "vicious assault" involved a regime artillery and tank barrage on a residential neighbourhood, she said.
"Those who perpetrated this atrocity must be identified and held to account. And the United States will work with the international community to intensify our pressure on Asad and his cronies, whose rule by murder and fear must come to an end," Clinton said in a statement.