Syrian security forces shot dead at least seven protesters on Friday in the flashpoint town of Daraa, a rights activist said as thousands rallied for democracy for a fourth week after Muslim prayers.
The authorities said two people were killed.
The rights activist, asking not to be named for security reasons, told AFP by telephone that seven people were killed when security forces opened fire with rubber bullets and live rounds to disperse stone-throwing protesters.
"Thousands of demonstrators leaving from three mosques marched to the courthouse but security forces dressed in civilian clothing fired tear gas to disperse them," said the activist.
"Demonstrators threw stones and clashes ensued," the activist said, adding that "the situation is very tense" in Daraa, some 100 kilometres (60 miles) south of Damascus.
He said the death toll could be higher than 10, although he had been able to confirm the identities of seven fatalities so far.
Protesters angered by the deaths set fire to the ruling Baath party's headquarters in Daraa, he added.
State television said "saboteurs and conspirators opened fire on residents and security forces" alike in the town, killing two people -- an officer and an ambulance man.
The official SANA news agency said dozens of civilians, security and police were wounded.
State television broadcast footage showing young men in keffiyehs standing behind trees while the sound of automatic weapons fire could be heard.
Daraa has been the focal point of anti-government protests marred by deadly violence which human rights activists blame on the security services and the government has attributed to an "armed" group.
President Bashar al-Assad, under popular pressure to introduce major political reforms and end emergency powers which give security services great leeway to crush dissent, had ordered a probe into previous protest casualties in Daraa.
Thousands of people on Friday also marched in five towns in northern Syria, mainly in predominantly Kurdish Hassake and Ammuda, calling for an end to emergency rule and the release of prisoners, another rights activist said.
"More than 3,000 people, Kurds, Arabs and Assyrians (Christians), demonstrated in Qamishli after Friday prayers before staging a sit-in on the main road," Kurdish rights activist Radif Mustafa told AFP.
"There were 2,000 (Kurdish) demonstrators in Ammuda, 1,500 in Deirbassiye, and hundreds in Hassake and two other districts... calling for the release of 200 Kurdish prisoners and the abolition of emergency law," he added.
The demonstrators chanted "God, Syria and freedom" and "Neither Arabs, nor Kurds, national unity," Mustafa said.
The rallies came one day after Assad granted citizenship to tens of thousands of Kurds who had been denied nationality for nearly half a century because of a controversial census.
Abdel Karim Rihawi, head of the Syrian League for the Defence of Human Rights, told AFP several thousand people demonstrated in the port city of Banias and Tal, 20 kilometres north of Damascus.
The rallies, he said, were staged in solidarity with the "martyrs" of protests in Douma, Daraa and Latakia, and demonstrators chanted "God, Syria and freedom."
In the industrial city of Homs, 160 kilometres north of Damascus, and in Harasta, near the capital, witnesses reported clashes between security forces and protesters.
In Douma, 15 kilometres north of Damascus, residents formed committees to verify the identities of people arriving for a rally to check they were not armed, a rights activist said.
He told AFP demonstrators and authorities had reached an agreement allowing protesters to rally without security force intervention.
"This agreement, so far, has been respected," he said.
New York-based Human Rights Watch said at least eight people, but perhaps as many as 15, were killed last Friday in Douma when men in civilian clothes, suspected by witnesses to be security services, fired at protesters.
The authorities blamed an unnamed "armed group."
Syrian rights activists estimate that more than 130 people have been killed in clashes with security forces, mainly in Daraa and the port city of Latakia, since the start of political unrest on March 15.
Officials have put the death toll at closer to 30 and blamed the violence on armed groups and foreigners seeking to divide the ethnically and religiously diverse country.