The Syrian army have been deployed to the southern city of Deraa as officials tried to calm passions following protests for freedom in which five civilians died, residents said.
Thousands of mourners marched at the funeral of 23-year-old Raed al-Kerad, the latest protester to be killed by security forces on Sunday. Mourners chanted slogans demanding political freedom and an end to corruption.
The mourners later gathered at the al-Omari mosque in the old quarter of Deraa near the border with Jordan.
Troops set up checkpoints at the entrances of Deraa and were checking identity cards. The Syrian justice minister arrived at a city hall.
Crowds set fire to a headquarters of the ruling Baath Party in the Syrian city of Deraa yesterday, as the wave of unrest in the Arab world shook even one of its most authoritarian states.
The demonstrators also set ablaze the main courts complex and two phone company branches. One of the firms, Syriatel, is owned by President Bashar al-Assad's cousin Rami Makhlouf.
"They burned the symbols of oppression and corruption," an activist said. "The banks nearby were not touched."
Assad, who has strengthened Syria's ties with Shia Iran as he sought to improve relations with the United States and strike a peace deal with Israel to return the Golan Heights, is facing the biggest challenge to his rule since he succeeded his late father, Hafez al-Assad, 11 years ago.
He has sent government officials to try to placate Deraa but thousands rallied to demand an end to emergency law in the southern city, on the third consecutive day of protests against Syria's ruling Baath Party.
"No, no to emergency law. We are a people infatuated with freedom," marchers chanted, despite the arrival in Deraa of a government delegation to pay condolences to relatives of victims killed by security forces in demonstrations there this week.
Security forces fired tear gas at the protesters. Around 40 people were taken to be treated for gas inhalation at the main Omari mosque in the old city, residents said.
"The mosque is now a field hospital. The security forces know they cannot enter the old city without spilling more blood," one resident said.
Syria has been under emergency law since the Baath Party, which is headed by president Bashar al-Assad, took power 1963 and banned all opposition.
Makhlouf is under specific US sanctions for what Washington regards as public corruption and has been a target of protesters chanting "thief". He owns several large businesses.
The protesters were in control of the old quarters of Deraa by nightfall, with heavy security presence in the rest of the city, which is near the border with Jordan.
Security forces opened fire on Friday on civilians taking part in a peaceful protest in Deraa demanding the release of 15 schoolchildren detained for writing protest graffiti, political freedoms and an end to corruption. Four people were killed.
An official statement said "infiltrators" claiming to be high ranking officers had been visiting security stations and asking security forces to fire at any suspicious gathering.
Citizens should report anyone suspected of trying to fool the security apparatus "into using violence and live ammunition against any suspicious gathering", the statement said.
The government sought to calm discontent by promising to release immediately the 15 children, who had written slogans on walls inspired by uprisings in Tunisia and Egypt.
The statement was a rare instance of Syria's ruling hierarchy responding to popular pressure.
Tens of people arrested on Friday have been released, but scores more were still in jail, activists said.
On Saturday, thousands of mourners called for "revolution" at the funeral of two of the protesters. Officials later met Deraa notables who presented then with a list of demands.
It included the release of political prisoners, dismantling of secret police headquarters in Deraa, dismissal of the governor, public trial for those responsible for the killings and scrapping of regulations requiring permission from the secret police to sell and buy property.