A Syrian artillery barrage killed more than 90 people, including dozens of children, in the worst violence since the start of a UN peace plan to staunch the flow of blood from Syria's uprising, activists said on Saturday.
The bodies of children were shown in footage posted to YouTube purporting to show the victims of the shelling in the central town of Houla on Friday. The sound of wailing filled the room.
The reports of the carnage, which could not be confirmed independently, underlined how far Syria is from any negotiated path out of the 14-month-old revolt against President Bashar al-Assad.
French Foreign Minister Laurent Fabius condemned the violence as a "massacre," and said he wanted to arrange a meeting in Paris of the Friends of Syria, a group that brings together Western and Arab countries keen to remove Mr. Assad.
Syrian state television aired some of the footage disseminated by activists, calling the bodies victims of a massacre committed by "terrorist" gangs.
A British-based opposition group, the Syrian Observatory for Human Rights, said residents of Houla were fleeing in fear of more shelling.
It said one person was killed in the northern town of Saraqeb when security forces opened fire on a protest against the killing. Activists distributed footage appearing to show similar protests in Aleppo, the largest city in the north.
A member of the fragmented exile group that says it speaks for Syria's political opposition said Assad's forces had killed "entire families" in Houla in addition to the shelling.
"The Syrian National Council (SNC) urges the UN Security Council to call for an emergency meeting ... and to determine the responsibility of the United Nations in the face of such mass killings," SNC spokeswoman Bassma Kodmani said.
Opposition activists said Syrian forces had opened fire with artillery on Friday after skirmishing with insurgents in Houla, a cluster of villages north of the city of Homs, itself battered by shelling.
Although Annan's six-week old ceasefire plan has failed to stop the violence, the United Nations is nearing full deployment of a 300-strong unarmed observer force meant to monitor a truce.
The plan also calls for a truce, withdrawal of troops from cities, and dialogue between the government and opposition.
Fabius said that "UN observers need to be able to complete their mission and the UN-Arab League's joint special envoy's exit plan has to be implemented immediately."
In a statement Arab League head Nabil Elaraby called the killing in Houla a "horrific crime," urging the UN Security Council - where Russia and China have protected Syria - to "stop the escalation of killing and violence by armed gangs and government military forces."
The state news agency SANA said the observers had visited Houla on Saturday, but did not elaborate. A spokeswoman for the monitoring mission did not respond to calls.
Syria calls the revolt a "terrorist" conspiracy run from abroad, a veiled reference to Sunni Muslim Gulf powers that want to see weapons provided to an insurgency led by Syria's majority Sunnis against Assad, a member of the minority Alawite sect.
UN Secretary-General Ban Ki-moon said on Friday that recent bomb attacks may have been the work of "established terrorist groups" and urged states not to supply arms to either the government or rebel forces.
"Those who may contemplate supporting any side with weapons, military training or other military assistance, must reconsider such options to enable a sustained cessation of violence," he told the Security Council in a letter.
The United Nations has accused Assad's forces and insurgents alike of grave human rights abuses, including summary executions and torture.
Ban has also expressed fear that Syria's conflict will destabilize neighboring Lebanon, whose delicate sect-based politics has been shaken by tensions among Lebanese foes and friends of the uprising in Syria.
In the latest episode, gunmen in northern Syria snatched a group of Lebanese Shiites this week as they were returning from a religious pilgrimage, sparking the worst unrest in years in the Lebanese capital.
Uncertainty over their fate increased tension in Beirut on Saturday, a day after Lebanon's top officials said the release of the hostages and their return home was imminent.
The prime minister said on Friday afternoon they had been freed, but by Saturday there was still no sign of them. A member of the SNC said they were still in captivity, further angering a crowd that had gathered at Beirut's airport to meet them.