Upon his arrival in Damascus, Syria, joint U.N.-Arab League special envoy Kofi Annan called Monday for those responsible for Friday's massacre of 108 people in the town of Houla to be held responsible and for his six-point plan to be implemented.

"This was an appalling crime, and the Security Council has rightly condemned it," he said in a statement.

"Those responsible for these brutal crimes must be held accountable. I understand that the government is also investigating. It is the Syrian people, ordinary citizens of this great country, who are paying the highest price in this conflict.

"Our goal is to stop this suffering. It must end and it must end now."

Annan demanded that the government of Bashar al-Assad "take bold steps to signal that it is serious in its intention to resolve this crisis peacefully, and for everyone involved to help create the right context for a credible political process. And this message of peace is not only for the government, but for everyone with a gun."

He added, "The six-point plan has to be implemented comprehensively. And this is not happening."

Annan said he plans to have "serious and frank" talks with al-Assad and others. He has met with the country's foreign minister, according to images broadcast on state TV.

But a rebel leader said Annan's six-point plan is already "dead" following the killings in Houla, a suburb of the anti-government bastion of Homs. U.N. monitors in Syria said 49 children were among the dead.

Al-Assad's regime insists it was not behind the massacre and blames terrorist groups. Throughout the uprising against the government, Syria has blamed violence on "armed terrorist groups."

Opposition leaders say the massacre is the latest in Syria's crackdown against protesters.

Syrian U.N. representative Bashar al-Jaafari, who called the deaths "an appalling, horrific unjustified and unjustifiable crime," insisted Monday that the Syrian government is working to find the people responsible. He called on the U.N. Security Council to "convene to define those who arm, host, harbor and encourage the terrorist groups to continue their violence in Syria and bring them to justice," the state-run news agency SANA reported.

Jaafari railed against "member states" of the Security Council who are helping the opposition. "Those who are very interested in halting violence and making the comprehensive national dialogue in Syria a success should stop interfering in our internal affairs and should stop arming, hosting, funding and protecting the armed terrorist groups in my country," he said.

British Foreign Secretary William Hague, who has expressed outrage about the massacre, was in Russia on Monday seeking to persuade Russian officials to pressure the Syrian regime to comply with Annan's peace plan.

But after Hague met with Russian Foreign Minister Sergey Lavrov, there was no clear sign that international action would ratchet up.

"It sounds very noble to say Russia is supporting the Syrian government, and when it stops supporting the Syrian government, everything will be fine," Lavrov told reporters.

But in reality, he said, "We do not support the Syrian government. We are supporting the Kofi Annan plan that addresses both the Syrian government and the armed opposition. ... We have to be objective."

After Friday's massacre in Houla, rebel leaders once again implored the international community for airstrikes against regime forces.

Meanwhile, residents of Houla were grieving as opposition activists and residents blamed al-Assad's regime for the bloodbath.

"By God, I washed the dead bodies of nine children. One was less than 9 months old!" a man screamed to a U.N. observer. "Why are they treating us like animals? We are humans. Did the infant carry an RPG? Was he a fighter? It was a baby, he had a pacifier in his mouth."

Images from Houla show a room crammed with the mangled and bloody bodies of children -- some with their skulls torn open.

"After the stuff we've seen, we can't feel anything. ... We're used to the sights now, the blood, the sound of gunfire," said another resident, who CNN is not naming because of safety concerns.

Pro-government gangs have returned to Houla, where food, water and medicine are in short supply, he said.

"They only thing we have here is the Free (Syrian) Army. It's the only thing that can protect us after God," the resident said.

The killings reignited international fury against al-Assad's regime for its 14-month crackdown on dissidents seeking an end to his rule.

On Sunday, some U.N. Security Council members condemned the Houla attacks "that involved a series of government artillery and tank shellings on a residential neighborhood" as well as the killings of civilians by gunshots fired at close-range.