At least 20 killed near Daraa, a witness tells Al Jazeera, as anti-government protesters defy security crackdown.

The bloody crackdown on protesters in Syria has left dozens dead as President Bashar al-Assad faces the greatest challenge to his 11-year rule.

Security forces opened fire on anti-government protesters in the city of Sanamin near Daraa on Friday, killing at least 20 people, according to one witness.

"There are more than 20 martyrs .... they [security forces] opened fire haphazardly," the witness told Al Jazeera on Friday.

Rula Amin, Al Jazeera's correspondent in Damascus, said Syrian forces apparently fired after protesters set fire to a statue of the late president, Hafez al-Assad.

Footage on YouTube also showed protesters in the cental square of Daraa dismantling a portrait of his son, Bashar al-Assad, the current president.

Reuters reported that heavy gunfire could be heard in the southern city of Daraa, the focal point for demonstrations against Bashar al-Assad's regime in recent days.

Three people were also reported killed in Mouadamieh district of Damascus after a crowd confronted a procession of cars driven by supporters of president Bashar al-Assad, residents said, according to Reuters.

Regime supporters take to streets

But regime supporters also took to the streets in sizeable numbers on Friday, waving flags and images of al-Assad. A large crowd gathered in the evening outside Al Jazeera's bureau in Damascus, demanding to be shown on the network.

"Thousands and thousands are now out in the streets of the capital, driving around the capital, showing their support for President Aasad. There is no doubt the president does have support in this country. Bashar al-Assad is a popular leader," said Al Jazeera's correspondent Zeina Khodr.

But Anas al-Abda, the chairman of the Movement for Justice and Development in Syria, told Al Jazeera that pro-government demonstrations were "most probably fabricated and organised by the regime".

Earlier, Reem Haddad, from the Syrian information ministry, told Al Jazeera that security forces had been given the order not to shoot at protesters "no matter what happens".

"But things took on a different hue because inside these peaceful demonstrations there was another group of people who were armed ... and were shooting at the security forces and were shooting at other citizens in Daraa. At the end of the day this became a matter of national security."

But an eyewitness told Al Jazeera that "there were no people carrying arms among demonstrators".

"What happened in the square ... was live ammunition, I was present myself and I saw the youth and other young demonstrators leading a peaceful demonstration.

"They were chanting slogans calling for freedom and transparency and an end [to] corruption."

'Day of dignity'

The latest clashes come after protesters demanding greater freedom called for a "day of dignity" on Friday following a week-long crackdown by pro-regime forces that has left dozens dead.

At least 200 people marched in the centre of Damascus after Friday prayers in support of the people of Daraa, scene of protests against Baath Party rule, Reuters reported.

Protests spread across Syria, with rallies also held in the central city of Hama and in Tel, near Damascus. According to our correspondent, numbers at these rallies ranged from hundreds of people to thousands.

Daraa, the main city of southern Syria, has become a flashpoint for protests. Officials have been on the defensive after protesters in the southern city were shot dead by police.

The crackdown has already attracted the attention of the United Nations with human rights commissioner Navi Pillay calling for an investigation and an immediate halt to violence, a message echoed by Ban Ki-moon, the UN Secretary-General.

Human rights group Amnesty International said on Friday that at least 55 people had been killed since protests erupted.

The US on Friday called on the Syrian government to end the use of violence against protesters and the arrests of human rights activists.

"We strongly condemn the Syrian government's attempts to repress and intimidate demonstrators," said White House spokesman Jay Carney.

Britain also expressed concern. "I call on the Syrian government to respect the people's right to peaceful protest and to address their legitimate grievances. I call for restraint on all sides but in particular from the Syrian security forces. Violence is never the right answer to these situations." said Alistair Burt, a foreign office minister.

On Thursday, Syrian government announced that it would "study" ending emergency rule - in place since 1963 - and look into legalising political parties.

The current emergency law allows people to be arrested without warrants and imprisoned without trial.