At least 12 mourners have been killed in Syria as pro-democracy protesters buried their dead after the bloodiest day yet of an uprising against the country's authoritarian government. Two politicians also resigned from parliament in a sign of growing unease at the government's use of lethal force.

Nasser al-Hariri, a member of Syria's parliament from Deraa, told al-Jazeera Arabic TV: "I can't protect my people when they get shot at so I resign from parliament." Minutes later a second politician, Khalil al-Rifae, also from Deraa, resigned live on the channel.

The resignations – the first during this crisis – were a significant sign of unease at escalating violence. Security forces again opened fire at funerals for Friday's victims, where large crowds of mourners were chanting anti-government slogans.

A witness in Izraa told the Observer that five people from nearby Dael and Nawa were shot dead at the entrance to the town . "They were attempting to come to the funerals of 10 people killed on Friday," he said. He insisted the security forces and army were responsible. News agencies reported that at least two mourners had been shot dead by snipers in Douma, a suburb of Damascus, and three in the district of Barzeh.

Human rights organisations and activists said at least 76 people and possibly more than 100 were killed during the largest and bloodiest protests yet on Friday, as the unrest continued into its eighth week. Many were shot in the head and chest, and mosques were used as hospitals. Al-Jazeera reported accounts of Syrian security officers entering hospitals and clinics to take the dead and injured to military hospitals in an apparent attempt to cover up casualty figures.

Local human rights organisations claimed some Syrian Christians were among the dead. Christians, who make up around 10% of Syria's population of 22 million, are largely supportive of the regime due to fears of a backlash by the Sunni Muslim majority. The claims could not be independently verified. Easter celebrations, in which parades of children and families usually flood the streets of Damascus's old city, have been cancelled. It is unclear whether this was a decision by Christian leaders or if the government had put pressure on them in a bid to prevent large gatherings.

With the death toll since 18 March now above 280, international condemnation of Syria has begun to grow. Barack Obama issued a strongly worded statement calling the violence "outrageous" and said that it should "end now". As in other protests that have swept the Arab world, social media have been one of the powerful tools of protest, subverting official channels. Amateur video footage of bloody scenes continued to emerge from the protests.

In one video, posted on YouTube, a man tells how security forces killed his son and left him to die.

As the situation escalates, Syrian observers said the government had made it clear that it intended to cling to power with the use of violence, despite attempts at reform. "They want to push demonstrators to the limits," said Ayman Abdel Nour, a Syrian dissident based in Dubai. He still believed that President Bashar al-Assad had time to show that he was serious about reform.

But after Assad recently lifted the country's state of emergency, abolished the security court and appointed new governors in Latakia, Homs and Deraa, other commentators said he was running out of options.

Protesters have responded with a new round of chants. "We want the toppling of the regime," said a resident of Ezraa, a small southern town that saw one of the highest death tolls on Friday. "The blood of our martyrs makes this our responsibility now."

Activists acknowledged some concerns that protesters, who have been overwhelmingly peaceful so far, will be tempted to take up arms in self-defence. Syrians say weapons licences are hard to come by for non-Baath party members, but many people in the tribal southern region own guns.

The regime still retains the loyalty of the military and leading businessmen as well as many among the country's minority communities. In the streets of central Damascus, many say they would rather stick with stability than take a risk on what would come if Assad's regime was to fall.

Syria's government, which has continued to blame the deaths on armed gangs, expressed "regret" at Obama's sharp condemnation of Friday's violence. "It isn't based on a comprehensive and objective view of that is happening," it said in a statement posted on the official Sana website.

It added that Syria viewed Obama's comments as "irresponsible".

The statement came as al-Jazeera correspondent Cal Perry was ordered to leave the country, adding to an almost total blackout on independent and foreign media.

Katherine Marsh is the pseudonym of a journalist living in Damascus