(CNN) -- Syrian government forces pounded the central province of Homs on Friday, killing 88 people -- some of them children -- an opposition group said.
"This barbaric act was preceded by the regime's mortar shelling in the town," the Local Coordination Committees of Syria (LCC) said in a statement, referring to Hawleh, a town in the suburbs of Homs. "The campaign ended when the armed militias slaughtered entire families in cold blood."
The group described the attack as a massacre.
"We in the Local Coordination Committees are pained by the international community's apparent blindness to the bloodshed, and believe the United Nations Security Council (UNSC) bears the responsibility for its inability to protect Syrian civilians. We request that the UNSC now take a step forward and more forcefully express its position with regard to the regime's practices," the group said.
Another opposition group, the Syrian Observatory for Human Rights, said more than 300 people were wounded in the onslaught and that 13 children were killed.
"It's unbelievable that we have seven billion people on this planet, and they all can't do anything about what they are seeing on TV," Abu Emad, an activist, told CNN from Homs.
"Do something," he begged the international community.
Graphic video posted on YouTube purports to show the lifeless bodies of several small children killed in Hawleh. 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 can be heard shouting.
CNN could not independently confirm the authenticity of the video.
In other clashes, at least 10 civilian and opposition fighters were injured in a reported assault on the area known as the Mountain of the Kurds near the Turkish border, the Syrian Observatory for Human Rights reported. Four government troops died, the group said.
Helicopters fired Friday night on several locations in Idlib province, including Kinda village, Kabaneh, Aako and Abu Risha in Jabal Akrad, according to the LCC. Several people were reportedly wounded, the group said.
Government forces also shelled opposition sites in the Homs neighborhoods of Sultanieh and Jobar as people gathered for Friday protests, opposition activists said.
In Aleppo, armored vehicles were seen in the streets for the first time since the uprising in Syria began in March 2011, the Syrian Observatory for Human Rights reported.
CNN cannot independently confirm reports from within Syria because the government strictly limits access by foreign journalists.
In another development Friday, 11 Lebanese Shiite pilgrims abducted in Syria were freed, Lebanese Prime Minister Najib Mikati's office said in a statement. They were in Turkey on Friday and were expected back in Beirut shortly, according to the statement.
The pilgrims -- all men -- were detained Tuesday by an armed group in northern Syria soon after crossing the border from Turkey. They were on their way back from visiting holy sites in Iran.
The incident raised tensions in Lebanon, with protesters in the mainly Shiite areas of southern Beirut taking to the streets Tuesday and Wednesday.
Meanwhile, the United Nations said there is no fallback plan to deploying monitors to some of the nation's most embattled cities.
U.N. monitors on the ground in five cities are making "all possible efforts to stop violence" and have had "some dampening effect," Secretary-General Ban Ki-moon told CNN's Christiane Amanpour.
However, they have not managed to halt the violence, he said.
Ban said the full cadre of observers -- 300 -- authorized by the United Nations Security Council last month would be on site in the coming days.
"They are patrolling every day, whenever possible," he said. "They try their best to cease this violence. It requires strong political will at the level of President Assad, and also it requires full cooperation by the opposition forces."
As protests continue, a report by the Independent International Commission of Inquiry on Syria noted the growing power of forces opposed to President Bashar al-Assad.
"Whereas government forces had previously been responding primarily to demonstrations, they now face armed and well-organized fighters -- bolstered by defectors who joined them," the report said.
"Gross violations continue unabated," the commission's report said, adding that regime forces commit most of the human rights violations.
Violence has raged daily. About 40 civilians were killed across the country Thursday, the LCC said. Most of the deaths were in the provinces of Homs, Hama and Idlib.
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.
The commission said abuses have mounted since March, even though al-Assad's government and opposition forces said they have embraced U.N. and Arab League envoy Kofi Annan's six-point peace plan that includes a cease-fire.
The report pointed to bombing attacks in Damascus, Aleppo and Daraa between March and May, including suicide car bombings in Damascus on May 10 that left 55 people dead.
The report was issued as Syria's newly elected parliament convened to elect a speaker and swear in new members. The government said the elections were all-inclusive, but opposition forces call the process a sham.
CNN's Richard Roth, Hamdi Alkhshali, Joe Sterling, Nada Husseini, Amir Ahmed and Kamal Ghattas contributed to this report.