The bound bodies of 13 people, some showing signs of being shot at point blank range, have been found in eastern Syria, according to the United Nations.
The head of the UN observer mission to Syria, Major-General Robert Mood, said the victims had been discovered with their hands tied behind their backs.
In a statement the veteran Norwegian peacekeeper said he was "deeply disturbed by this appalling and inexcusable act."
"He calls on all parties to exercise restraint and end the cycle of violence for the sake of Syria and the Syrian people," a statement released on Maj-Gen Mood's behalf said.
It has emerged that the bodies were discovered on Tuesday night in the area of Assukar, 30 miles east of Deir Ezzor.
The latest discovery has given further importance to the UN Human Rights Council special session being held on Friday to probe the May 25 massacre in Houla.
The UN said at least 108 civilians died in the attack, including 49 children and 34 women, amid fears of widening sectarian bloodletting.
Survivors have told harrowing stories of the killings, with one child describing how his entire family were shot dead.
Meanwhile, tit-for-tat diplomatic expulsions have occurred in Damascus, neighbouring Turkey and at least 11 foreign capitals.
China and Russia have also voiced their opposition to any UN Security Council backed military action in Syria.
"We believe that a review now by the Security Council of any new measures on the situation would be premature," Russia's deputy foreign minister Gennady Gtilov said.
Russia also condemned the diplomatic expulsions as "counterproductive".
Strategically important Turkey has told Syria to withdraw all its diplomats from Ankara within 72 hours and warned it and the international community will take further "measures" if crimes against humanity continue.
China's foreign ministry also reiterated its opposition to military intervention, as UN and Arab League envoy Kofi Annan's "frank" talks with Syria's President Bashar Assad warned of a "tipping point" being reached.
Spokesman Liu Weimin also stopped short of saying whether China would expel Syrian diplomats over the massacre.
Although French president Francois Hollande said military action against Syria could be launched - a position supported by newly confirmed US Republican Party presidential candidate Mitt Romney - the White House downplayed direct military action.
The US continues to exert economic pressure on the regime and on Wednesday announced sanctions against the Syria International Islamic Bank, which is believed to be a money conduit for the Assad elites.
Mr Annan's deputy, Jean-Marie Guehenno, told the UN Security Council this afternoon that the uprising is unlikely to stop without political negotiations between the government and opposition.
"(The) uprising in Syria has the characteristics of a revolutionary movement," a diplomat told Reuters, summarising remarks from Mr Annan's deputy.
New details have emerged of the Syrian gunmen allegedly behind the massacre, as UN peacekeeping chief Herve Ladsous said there are strong suspicions that militia loyal to President Bashar Assad were responsible for some of the killings.
He said there was no reason to believe that "third elements" - or outside forces - were involved after the Syrian regime denied any role and blame the killings on "armed terrorists".
It claimed the assailants attacked army positions in the area and slaughtered innocent civilians, but has provided no evidence to support its case, nor has it given a death toll.
But according to witnesses the massacre in the Sunni village last Friday, 25 miles north west of the city of Homs, had dangerous sectarian overtones.
"It's very hard for me to describe what I saw, the images were incredibly disturbing - women, children without heads, their brains or stomachs spilling out," a Houla resident who hid in his home during the attack said.
He said the pro-regime gunmen, known as shabiha, targeted the most vulnerable in the farming villages that make up the poor area of Houla.
"They went after the women, children and elderly," the resident, who asked that his name not be used out of fear of reprisals, said.
Shabiha fighters, part of the Alawite sect to which the Assad family and the ruling elite also belong, have spread fears they will be persecuted if the Sunni majority gains the upper hand.
Sunnis make up most of Syria's 22 million people, as well as the backbone of the opposition which is claimed to be entirely secular.
In some cases, the unnamed resident said, neighbours who have lived side-by-side for years are turning on each other driven by sectarian hatred.
The volatile religious divide makes civil war one of the most dire scenarios, feared by UN and Arab League envoy Mr Annan.
Mr Annan said: "We are at a tipping point. The Syrian people do not want the future to be one of bloodshed and division. Yet the killings continue and the abuses are still with us today.
"Let me stress once again: the violence must stop and the six point plan must be implemented. I need the president to act now. I need other parties to do their part."