U.N. mission chief in Syria Maj. Gen. Robert Mood, speaking Saturday in Damascus, called the use of force "unforgivable."

(CNN) -- More than 92 people, including 32 children younger than 10, were killed Friday by artillery tank shells in the Syrian village of Houla, a spokesman for the joint special envoy to Syria said Saturday.

United Nations observers went to Houla and viewed the bodies Saturday, a day after opposition activists reported a massacre there at the hands of the Syrian regime. The activists said entire families were killed.

Maj. Gen. Robert Mood, the head of the U.N. Supervision Mission in Syria, said the attacks happened overnight but that the circumstances that led to the deaths is unclear.

"This indiscriminate and disproportionate use of force is unacceptable and unforgivable," Mood said in a statement provided by Ahmad Fawzi, the spokesman for envoy Kofi Annan. "The killing of innocent children and civilians needs to stop."

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Syrian opposition activists reported at least 88 people, mostly children, were killed Friday by the Syrian regime's mortar shelling in Houla. The reports came from the Local Coordination Committees of Syria, a network of Syrian opposition activists.

Britain condemned the massacre, calling Saturday for an urgent session of the U.N. Security Council and a full account of the "appalling crime."

More regime attacks Saturday killed 43 people across the country, including 20 in Homs, just south of Houla, according to the Local Coordination Committees.

A caller to Syrian state television Saturday blamed the Houla massacre on criminal gangs and terrorist groups. An analyst on the station said al Qaeda and its branches are to blame and that "the Syrian military is the defender of the nation."

The state-run Syrian Arab News Agency reported the observers' visits Saturday to several towns and cities but made no mention of their visit to Houla or the deaths there.

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The Local Coordination Committees earlier Saturday decried the world's "apparent blindness" to the violence in Syria.

Months of U.N. Security Council attempts to resolve the crisis have failed to have any effect.

U.N. Secretary-General Ban Ki-moon said Friday the full cadre of 300 U.N. observers authorized by the Council will be in Syria in the coming days.

Ban issued a sobering report Friday on the Syrian crisis, detailing "continuing reports of a stepped-up security crackdown by the authorities that has led to massive violations of humans rights ... including arbitrary arrests, torture, enforced disappearance and summary execution of activists, opponents and defectors."

In a letter to the head of the U.N. Security Council, obtained by CNN, Ban said he is deeply concerned that the Syrian violence has not stopped despite the presence of the monitors and the agreement by both sides to a peace plan.

Some of the violence has abated when the monitors are around, he said, but across the country the level of it is high.

The monitors have seen "considerable" physical destruction across Syria, Ban said. They have also seen continued Syrian Army troop concentrations and heavy weapons in population centers, in direct violation of the peace plan forged by Annan in March.

Both sides blame the other for the destruction the monitors have seen, Ban said.

Some cities appear to be under opposition control, but Ban said residents are often too scared of reprisal to talk to the monitors, or they threaten the U.N. staff out of frustration with the ongoing crisis.

Ban said another key part of Annan's plan calling for the government to speed up the release of arbitrarily detained people hasn't happened. He said it was "unacceptable" that U.N. staff are unable to investigate numerous reports of detained or missing people.

Neither the government nor the opposition are granting total freedom of movement for journalists, and the regime is not allowing people to demonstrate peacefully, Ban said. Both are required under the peace plan.

As reports of deaths mount every day, so do the frustration and anger.

"It's unbelievable that we have 7 billion people on this planet, and they all can't do anything about what they are seeing on TV," activist Abu Emad told CNN from Homs early Saturday.

"Do something," he begged the international community.

Graphic video posted on YouTube purportedly shows the lifeless bodies of several small children killed in Houla. They are spread on the floor amid blankets, caked in blood. One child is turned to reveal a head wound.

"Look, these are just children. It is a massacre!" a man shouts.

CNN could not independently confirm the authenticity of the video, nor can it confirm reports from within the country because the government strictly limits access by foreign journalists.

U.N. officials say more than 9,000 people, mostly civilians, have died and tens of thousands have been uprooted since the uprising began in March 2011. Opposition groups report a death toll of more than 11,000 people.

Since al-Assad's government and opposition forces accepted Annan's peace plan in March, at least 1,635 people have been killed, the LCC said Saturday.

Following the reported massacre in Houla on Friday, the rebel Free Syrian Army implored members of the international "Friends of Syria" group to form a military coalition to launch airstrikes against al-Assad forces.

CNN's Elizabeth Joseph, Richard Roth, Saad Abedine, and Holly Yan contributed to this report.