Syria's main human rights movement said the death toll from pro-democracy protests against President Bashar al-Assad had reached 200 and urged the Arab League to impose sanctions on the ruling hierarchy.

Syria, the latest Arab country shaken by mass uprisings against authoritarian rulers, has witnessed unprecedented protests across the tightly-controlled country for the last three weeks.

Assad has responded with force - witnesses say security forces have opened fire on protesters - vague pledges of reform and attempts at appeasing minority Kurds. Protests have shown no sign of abating but have not yet reached the levels seen in Tunisia and Egypt where leaders were ultimately overthrown.

'Syria's uprising is screaming with 200 martyrs, hundreds of injured and a similar number of arrests,' the Damascus Declaration group said in a letter sent on Monday to the secretary general of the Arab League.

The Damascus Declaration is named after a document signed in 2005 by prominent civic, Islamist and liberal leaders calling for the end of 41 years of Assad family rule and its replacement with a democratic system.

'The regime unleashes its forces to besiege cities and terrorise civilians, while protesters across Syria thunder with the same chant 'peaceful peaceful',' it added.

'We ask you to impose political, diplomatic and economic sanctions on the Syrian regime, which continues to be the faithful guardian of Hafez al-Assad's legacy,' the letter said, referring to the iron-fisted rule of President Hafez al-Assad, who died in 2000 after 30 years in power.

The protests, which erupted in the southern city of Deraa last month before spreading, have demanded freedom of expression and assembly and an end to corruption.

The authorities blame 'armed groups' and 'infiltrators' for the violence, in which they said soldiers and police have also been killed. On Tuesday, state news agency Sana named six security service personnel it said had been killed and 168 wounded in Deraa, suburbs of Damascus, Homs and Latakia.

'President Assad has been only giving promises for the last 11 years. Instead of solutions he talks, as the regime usually does, about an outside conspiracy,' the letter said.

Last Friday was one of the deadliest since the uprising began in Deraa, an agricultural city near the border with Jordan where the majority tribes resent the wealth and power amassed by minority Alawites, the sect to which Assad belongs.

Human Rights Watch, which said 27 people were killed in Deraa, condemned Syria's security forces for preventing wounded protesters reaching hospitals and stopping medical teams from treating them in two towns.

'The Syrian authorities are responding to protests against repression with more repression: killings, mass arbitrary arrests, beatings and torture,' HRW's Sarah Leah Whitson said.

HRW said protesters told the rights group that demonstrators seized weapons from an abandoned army checkpoint and shot at security forces, killing at least a dozen of them and setting on fire two cars belonging to the army and security services.

Western governments who have been trying to coax Syria out of its anti-Israeli alliance with Iran as well as to give up its support for militant groups Hamas and Hezbollah, have denounced the violence against the protesters and urged Assad to take more vigorous steps towards reforms such as lifting emergency law.

'Time is running out as every new casualty makes the clock tick faster,' said the International Crisis Group's Peter Harling on the Foreign Policy blog.

'To open the space required for a radical reform agenda to take hold, the regime's top priority must be to ensure a period of relative calm. Prospects will look grim were the country to witness yet another bloody Friday,' he said, describing Syria as a 'slow-motion revolution'.

Assad has said the protests are part of a foreign conspiracy to sow sectarian strife. His father used similar language when he crushed leftist and Islamist challenges to his rule in the 1980s, killing thousands.

Syrian security forces sealed off the coastal city of Banias on Monday following pro-democracy protests and killings by irregulars loyal to Assad, residents said.

Since the uprisings in Tunisia and Egypt, authorities have intensified a campaign of arrests against dissidents and civic activists. Authorities generally embark on a round of arrests after protests, according to activists and witnesses, before later releasing some.

Fayez Sara, a journalist who was jailed for two-and-a-half years along with 11 Damascus Declaration members and released in 2010, was arrested again on Sunday, rights activists said.

'The secret police have been rounding up every outspoken figure they can get their hands on. They either call them in for 'interrogation' and keep them, pick them up from the street or break into their homes,' one of the rights defenders said.

Most of the Damascus Declaration members have spent long periods as political prisoners, including leading opposition figure Raid al-Turk, who spent more than 17 years in solitary confinement under Hafez al-Assad.-Reuters