President Bashar Assad's forces pounded rebel-held areas in central Syria on Friday, killing at least 22 people, activists said. More than 60 nations meeting in Tunisia asked the United Nations to start planning for a civilian peacekeeping mission that would deploy after the Syrian regime halts its crackdown.

As government troops relentlessly shelled rebel-held neighborhoods in the besieged city of Homs, thousands of people in dozens of towns staged anti-regime protests under the slogan: "We will revolt for your sake, Baba Amr," referring to the Homs neighborhood that has become the center of the Syrian revolt. Activists said at least 50 people were killed nationwide.

In Tunisia, the U.S., European and Arab nations asked the U.N. to start drafting plans for a civilian peacekeeping mission that would deploy after the Damascus regime halts the brutal crackdown.

Still unwilling to commit to military intervention to end the bloodshed, the group offered nothing other than the threat of increasing isolation and sanctions to compel compliance from Assad, who has ignored similar demands.

In Washington, President Barack Obama said the U.S. and its allies would consider "every tool available" to stop the slaughter of innocent people in Syria. He did not give specifics about what that might entail.

"It is time for that regime to move on. And it is time to stop the killing of Syrian citizens by their own government," he said.

On Thursday, former U.N. secretary-general Kofi Annan was appointed the joint United Nations-Arab League envoy on the Syrian crisis.

Annan said in a statement Friday that he would try to "help bring an end to the violence and human rights abuses, and promote a peaceful solution" in Syria. He expressed hope that the Syrian government and opposition groups will cooperate with him in his efforts.

The Tunisia meeting is the latest international effort to end the crisis, which began when protesters inspired by uprisings sweeping across the Arab world took the streets in some of Syria's impoverished provinces nearly a year ago to call for political change.

Assad's security forces have responded with a fierce crackdown, and blame the violence on Islamic extremists and armed gangs. In recent months, the situation has grown increasingly militarized as opposition forces, boosted by army defectors, have increasingly taken up arms against the regime.

The U.N. estimated in January that 5,400 people were killed in the conflict in 2011. Hundreds more have died since. Syrian activists say the death toll is more than 7,300. Overall figures cannot be independently confirmed because Syria has prevented most media from operating inside the country.

On Thursday, U.N.-appointed investigators in Geneva said they had compiled a list of Syrian officials accused of crimes against humanity in the crackdown. The list reaches as high as Assad.

While the U.S., EU and Arab League have ratcheted up the pressure on Assad, Russia and China have opposed foreign intervention or sanctions against Syria.

Alexei Pushkov, a Russian lawmaker, said Friday that in his recent meeting with Assad the Syrian president sounded confident and showed no sign he would he step aside. Pushkov warned that arming the Syrian opposition would fuel civil war.

"Assad doesn't look like a person ready to leave, because, among other things, there is no reason for him to do that as he is being supported by broad layers of the population," Pushkov said, according to the RIA-Novosti news agency.

Syrians demonstrating Friday condemned the positions of Russia, China and Iran -- countries whose governments have stood by the Assad regime.

"Iranian and Russian bullets are tearing apart our bodies," read a large banner unfurled in the town of Tibet el-Imam just north of the central city of Hama.

But in a move highlighting Assad's deepening isolation, the Hamas prime minister of Gaza voiced support for Syrian protesters seeking to overthrow his regime. It was the first time that a senior Hamas figure has publicly backed the uprising and rebuked the Syrian regime.

"We commend the brave Syrian people that are moving toward democracy and reform," Ismail Haniyeh told congregants after Friday prayers in Egypt's Al-Azhar Mosque, the country's pre-eminent Islamic institution.

Assad has long hosted and supported leaders of the Hamas movement, which rules Gaza, but the group has significantly reduced the presence of its exiled leaders in Syria in the wake of protests.

Four people died Friday in the renewed shelling of the Baba Amr neighborhood of Homs, activists said, the latest of hundreds killed there in recent weeks. The neighborhood has been under siege and intense shelling for three weeks.

A Red Cross spokesman said the group has evacuated seven people from Baba Amr to a hospital elsewhere in the city. Hicham Hassan said he did not know whether those evacuated included two foreign journalists who were wounded earlier this week.

The Britain-based Syrian Observatory for Human Rights said four others were killed in Homs' rebel-held neighborhood of Khaldiyeh while 14 were killed in shelling of the central Qarabeen neighborhood.

Amateur videos posted on the Internet by activists showed black smoke rising from residential areas of Baba Amr and debris littering its slum-like apartment blocks. Parts of Homs, Syria's third-largest city, have been under a fierce government attack for nearly three weeks.

The Observatory said troops were also attempting to storm Rastan, a besieged rebel-held town just north of Homs. He said the town was being shelled and reported heavy clashes between troops and army defectors who destroyed two armored personnel carriers.

The Observatory said 50 civilians were killed throughout Syria on Friday, including a father and his three sons in the central village of Kfar Alton in the province of Hama that came under intense government troops shelling.

The Local Coordination Committees activist network said 97 people were killed by security forces across Syria Friday, but the number could not be immediately confirmed by others.

In the northwestern town of Kfar Takharim, APTN video showed activists and youths demonstrating in the streets and chanting anti-Assad slogans.