Damascus: Syrian troops backed by tanks stormed the flashpoint town of Daraa on Monday killing at least 25 people, witnesses said, as a leading rights activist accused Damascus of opting for a 'military solution' to crush dissent.

Troops also launched assaults on the towns of Douma and Al-Muadamiyah near Damascus, witnesses said, as the head of the UN human rights agency slammed what she said was the Syrian security forces' disregard for human life.

Amman said Syria sealed off its border with Jordan in a statement quickly denied by a top Syrian customs official.

An activist in Daraa, Abdullah Abazid, said that Syrian forces were bombarding the town near the Jordanian border with heavy artillery and that "at least 25 martyrs have fallen."

"There are still bodies sprawled in the streets," he said as loud explosions and shooting could be heard in the background.

"They are pounding the town with heavy artillery and machine guns," Abazid said, adding that snipers posted on rooftops were also shooting.

Rights activists said a 3,000-strong military force swarmed into Daraa in the early hours of Monday with tanks taking up positions in the town centre and snipers deploying on rooftops.

A witness reported at least five bodies in a car that had been raked by gunfire.

A massive crackdown was also underway Monday in Douma, 15 kilometres (nine miles) north of Damascus, and nearby Al-Muadamiyah, rights activists said, reached by telephone.

The military assaults come as Syria is engulfed in anti-regime protests that have sparked security force crackdowns in which more than 360 people have been killed, according to rights activists and witnesses.

Of these, more than 140 people have died since Friday alone. The crackdown comes despite President Bashar al-Assad signing on Thursday decrees ending a draconian state of emergency, imposed by the Baath Party when it seized power in 1963, to placate more than a month of pro-democracy protests.

He also abolished the state security court that has tried scores of regime opponents outside the normal judicial system and issued a decree "to regulate" peaceful demonstrations.

Rami Abdel Rahman, a prominent rights activist told AFP that Monday's assaults showed Damascus had decided to crush the protests militarily.

UN High Commissioner for Human Rights Navi Pillay called on Syria to stop the use of violence against protesters.Tens of thousands swarmed cities and towns across Syria on Friday to test implementation of the reforms authorised by Assad a day earlier, but security forces used live rounds and tear gas against them, activists said.

Jordan's Information Minister Tahen Adwan, meanwhile, said Syria had "closed its land borders with Jordan", a few hours after the start of the assault on Daraa, which is situated around five kilometres (three miles) from the frontier.

But Syria's official news agency SANA cited the director general of customs, Mustapaha Bukai, denying the closing of the border and saying "all the border posts with our neighbours, including Jordan, are open."

The protests against Assad's regime started mid-March in Daraa and spread to other major centres, including the capital Damascus.

Syria blames "armed gangs" for the unrest aimed at fuelling sectarian strife among its multi-religious and multi-ethnic communities.