The grim discovery of a man who had been shot in the head with his hands tied behind his back near the Syrian capital Damascus led to a funeral protest at which security forces shot dead five people, activists have claimed.

The shootings are a sobering insight into protest that continue across the country, even as the rebel stronghold of Homs fell to President Bashar al-Assad's tanks and mortar fire.

According to Avaaz, Munir Ramadan was found dead in the town of Duma, just north east of Damascus. Videos posted to YouTube show dozens of people gathered for his funeral, before they are surrounded by security forces near to the Grand Mosque.

Once inside they were fired upon by security forces, Avaaz said, and five people were killed.

Meanwhile in Homs government forces took control after a sudden ground invasion followed more than three weeks of brutal shelling, which killed hundreds of civilians.

Around 4,000 residents in Baba Amr were left behind in fear of a "massacre", said the Syrian National Council.

An activist known as Abu Uday told Avaaz: "We fear that the army and security forces are going to commit a massacre in retaliation for their support for the Free Syrian Army (FSA). This is not a defeat for the revolution, the resilience of the residence of Baba Amr is an achievement belonging to the people of this district."

Snowfall in the city briefly slowed the advance of government tanks, but by Thursday evening the FSA was forced to withdraw.

Colonel Riyadh al Asaad, the leader of the FSA, said it had "pulled out tactically in order to protect the remaining civilians".

Amid warnings of further reprisals President Bashar al-Assad indicated he would now allow the International Committee of the Red Cross to enter the city.

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The Red Cross said a convoy of seven aid trucks was on the way to Homs from Damascus.

But British Prime Minister David Cameron said Assad's move to allow aid would not prevent his eventual "day of reckoning".

Speaking at an EU summit in Brussels, where it is expected that fresh sanctions will be imposed on the regime, Cameron said it was "vitally important" that humanitarian aid reached Homs.

He said: "What we are going to be discussing today though is the situation in Syria which is absolutely appalling and it is vitally important that there is humanitarian access in to Homs and elsewhere so that people can get the help they need.

"But above all, what I think matters, is building the evidence and the picture so we hold this criminal regime to account and make sure that it is held to account for the crimes it is committing against its people and that one day, no matter how long it takes, there will be a day of reckoning for this dreadful regime."

On Thursday Russia and China backed a UN statement criticising Assad's refusal to allow United Nations humanitarian chief Valerie Amos to inspect the country.

While both still insisted that the Free Syrian Army and other opposition groups bear a heavier responsibility for their part the violence, Russia signalled a shift in direction when leader Vladimir Putin said it was down to the Syrian people to decide their leader.

Putin, who is seeking a return to the presidency in elections this weekend, denied Moscow had any special relationship with Damascus.

He said in an interview with the Times newspaper: "When Bashar al-Assad came to power he visited London and other European capitals first. We don't have a special relationship with Syria.

"It is up to the Syrians to decide who should run their country. We need to make sure they stop killing each other."

Putin also urged the West not to become "emotional" as stories of violence and human rights abuses appeared in the media.

Elsewhere, Tunisian president Moncef Marzouki is prepared to offer asylum to Syrian leader Bashar al-Assad if he agrees to end the conflict, it was reported.

Marzouki has told a local French-language newspaper, La Presse, that the offer would also apply to other members of the government.

Tunisia was the first country to recall its ambassador from Syria and also hosted an international conference to condemn the violence on 24 February.

Its own president, Zine al-Abidine Ben Ali, was forced to leave office and flee the country in January 2011 after the country's own widespread protests at the start of what became known as the Arab Spring.

The Foreign Office also continued to assess the authenticity of videos posted by activists in Syria showing Sunday Times reporter Marie Colvin and French photographer Remi Ochlik being buried.

A man in the videos says the pair, killed last week in a rocket attack on the besieged Baba Amr district of Homs, were interred in a local cemetery because power shortages meant their bodies could not be preserved.