Syria has opened its main prison in Damascus to the Red Cross, the organisation said, a move that could help reveal the fate of some of the thousands detained since the start of a five-month uprising.

The announcement came on Monday as forces and militiamen loyal to President Bashar al-Assad killed at least 10 civilians across Syria on Monday in assaults to end pro-democracy protests and to stop refugees fleeing the bloodshed from crossing to Turkey, activists and residents said.

The International Committee of the Red Cross (ICRC) visits people in places of detention worldwide from Gaza to Guantanamo to assess their conditions of detention and treatment.

But its confidential findings are shared only with the authorities concerned, which human rights activists warn could diminish the impact of the visits.

Many people who have been rounded up or disappeared are being held in schools and factories which may be off-limits to the ICRC, they add.

'We know that there are more than 15,000 detainees who are not in the formal prisons, among them five of my relatives,' Radwan Ziadeh, a Washington-based Syrian exile and activist, told Reuters.

The ICRC said its officials visited detainees in the central prison in the Damascus suburb of Adra in an 'important step forward' to fulfil its humanitarian activities in Syria.

'The Syrian authorities have granted the ICRC access to a place of detention for the first time. Initially, we will have access to persons detained by the Ministry of the Interior and we are hopeful that we will soon be able to visit all detainees,' ICRC president Jakob Kellenberger said in a statement issued at the end of a two-day visit to Damascus.

Human rights campaigners say Syrian forces have arrested tens of thousands of people since the uprising demanding political freedom and an end to 41 years of Assad family rule erupted in March, with many being housed in security police buildings off limits to the ICRC, whose reports are not public.

They say a reported defection of the attorney general of the city of Hama, which was attacked by the military last month, could reveal details of human rights abuses, including shootings and torture of prisoners, which have intensified in the last month as protests spread.

A Syrian lawyer, who did not want to be identified for fear of reprisals, said the Red Cross needed to have access to unofficial jails and detention centres to see torture chambers and the extent of human rights violations in the country.

'The Damascus central prison is mostly for criminal, not political cases. The bulk of the ugliest torture takes place in the cellars of secret police branches spearheading the repression, such as Military Intelligence and Air Force Intelligence,' he said.

Syrian authorities do not reveal the number of detainees in the country but they have previously denied torture allegations and said that any arrests were made in compliance with the constitution.

Syrian forces launched on Monday their biggest sweep against popular unrest in Syria's northwest near Turkey since June, killing a civilian in raids that have galvanised the West against President Bashar al-Assad.

Nine other civilians were killed in assaults on the city of Homs and its countryside, where tanks deployed four months ago after large protests demanding Assad's removal.

Four employees of the state-owned Syrian Petroleum Transport Company were also killed in Homs when unknown gunmen opened fire on a bus carrying them, the Britain-based Syrian Observatory for Human Rights, headed by dissident in exile Rami Abdelrahman, added in statement.

British Prime Minister David Cameron told parliament Assad had lost all legitimacy, joining the United States, France and other European countries that have said he must leave for Syria to become a democracy after four decades of autocratic rule.

Arab League chief Nabil Elaraby will visit Syria on Wednesday, Egypt's news agency Mena reported on Monday.

Elaraby had said the visit would be used to pass on Arab worries about the Syrian authorities' violent crackdown on protests against Assad's rule.

Protests again erupted in several large towns across southern syria after evening prayers on Monday, activists and residents said, citing the towns of Hirak, Inkhil, Jeza, Museifra and Teba where protesters numbering in the hundreds to thousands marched in anti -Assad demonstrations.

Frequency of protests in the countryside around Deraa have picked up this last week since the end of Ramadan, according to residents who say no longer restricted to Fridays as before.

In Deraa city, cradle of the uprising, heavy army and security presence made it more difficult for protesters to take to the streets but residents reported several smaller demonstrations in some neighbourhoods in which hundreds of youths took part, they said.

Fleeing to Turkey

In the northwestern province of Idlib, Adelsalam Hassoun, 24, a blacksmith, was killed by army snipers on Monday just after he had crossed into Turkey from the village of Ain al-Baida on the Syrian side, his cousin told Reuters by telephone from Syria.

'Abdelsalam was hit in the head. He was among a group of family members and other refugees who dashed across the plain to Turkey when six armoured personnel carrier deployed outside Ain al-Baida and started firing their machineguns into the village at random this morning,' Mohammad Hassoun said

Thousands of families fled their homes in the northern border region in June when troops assaulted town and villages that had seen big protests against Assad.

Faced with a heavy security presence in central neighbourhoods of Damascus and Aleppo, and military assaults against a swathe of cities from Latakia on the coast to Deir al-Zor in the East, street rallies calling for an end to the Assad family's domination of Syria have intensified in towns and villages across the country of 20 million.

Demonstrators have been encouraged by the fall of Libya's Muammar Gaddafi and growing international pressure on Assad.

The European Union has imposed an embargo on Syrian oil exports, jeopardising a major source of revenue for Assad, who inherited power from his father, the late Hafez al-Assad, in 2000.

'Economic pressure will be key in swaying the merchant class toward the side of the uprising, but Assad will keep adopting the military solution and deploying heavy weapons across Syria,' said Syrian dissident in exile Bassam al-Bitar.

'International intervention, something akin to a no-fly zone, will still be needed to protect protests and encourage more members of the army to defect,' Bitar, a former diplomat, told Reuters from Washington.-Reuters