The Syrian authorities on Friday called on people not stage demonstrations after anti-regime activists called for a "day of rage" across the country.
"In the current circumstances, the interior ministry calls on brother citizens to contribute in an effective way to stability and security... by not staging demonstrations or sit-ins for any reason without official permission," said a statement reported by the state news agency SANA.
"The laws in force in Syria will be applied to preserve the security of citizens and the country's stability," the ministry statement added.
Activists on Thursday called for "day of rage" protests across Syria after the Friday weekly Muslim prayers, piling pressure on President Bashar al-Assad as his regime pressed a violent crackdown on dissent.
The looming showdown comes as the UN Human Rights Council prepared for a special session on Syria in Geneva, and the European Union was meeting in Brussels to consider a wide range of sanctions against the Arab state.
The call for mass demonstrations was made in a statement on the Facebook page of Syrian Revolution 2011, a motor of the protests in which demonstrators inspired by uprisings elsewhere in the Arab world are seeking greater freedoms.
"To the youths of the revolution, tomorrow we will be in all the places, in all the streets ... We will gather at the besieged towns, including with our brothers in Daraa," said the statement.
It said demonstrations would also be staged in other flashpoint towns such as Homs in the centre of the country and Banias in the northwest.
Information Minister Adnan Mahmud told AFP that the crackdown on protesters would continue, setting the scene for violent confrontations later Friday.
Similar protests after Friday prayers a week ago ended in chaos, with more than 100 people killed when the security forces fired on demonstrators with tear gas and live rounds. Hundreds of people were detained.
"The authorities are determined to restore security, stability and peace to the citizens," Mahmud said. "In Daraa, the army intervened at the request of the population to restore security."
According to the minister, more than 50 soldiers and dozens of police have been killed and hundreds injured since the revolt began.
Syria has been rocked since March 15 by increasingly strident pro-democracy demonstrations, which the authorities have tried to crush through violence that rights groups say has killed at least 453 civilians.
In the southern town of Daraa, epicentre of the protests that have shaken Assad's once uncontested rule, water and power have been cut and the death toll has risen to 42 as a military siege enters a fifth day, rights activists said.
A rights activist reached by telephone said the situation was worsening in Daraa, stormed on Monday by between 3,000 and 5,000 troops backed by tanks and snipers.
"We have neither doctors nor medical supplies, not even baby milk. The electricity is always cut and we haven't any more water," Abdallah Abazid told AFP in Nicosia by telephone from Daraa, 100 kilometres (62 miles) south of Damascus.
At least 42 "martyrs" have been killed since Monday, Abazid said. Their families, he added, had been unable to bury them because "security forces were firing on anybody visiting the cemetery," which is controlled by the army.
In Washington, three key US senators urged President Barack Obama to declare that his Syrian counterpart Bashar al-Assad has squandered his legitimacy and must step down.
"We urge President Obama to state unequivocally -- as he did in the case of (Libyan leader Moamer) Kadhafi and (Egyptian President Hosni) Mubarak -- that it is time for Assad to go," Republican Senators John McCain and Lindsey Graham and independent Senator Joe Lieberman said in a joint statement.
The UN Human Rights Council meeting, requested by 10 European nations, the United States, Japan, Mexico, South Korea, Senegal and Zambia, will open at 11.00 am (0900 GMT).
A draft resolution tabled by Washington calls on the 47-member Council to agree to "urgently dispatch an independent, international commission of inquiry ... to investigate all alleged violations of international human rights law" in Syria.
The proposal also "strongly condemns the killing, arrest and torture of hundreds of peaceful protesters by the Syrian government" and "stresses the need to investigate... and prosecute those responsible for attacks."
New York-based Human Rights Watch called on the council to investigate the deadly crackdown on Syrian protesters and to "strongly condemn repression of peaceful protests."
"Syria’s President Bashar al-Assad needs to hear an unequivocal message from the Human Rights Council that violent suppression of peaceful protests is unacceptable and will have consequences," said Julie de Rivero, Geneva director at Human Rights Watch.
The European union meanwhile is eyeing a wide range of sanctions against Syria, from halting aid to an arms embargo and asset bans on officials involved in a brutal crackdown on protesters, diplomats in Brussels told AFP.
EU ambassadors meeting in Brussels on Friday will be mulling four sets of proposals set out by the 27-nation bloc's diplomatic service, including a suspension of 210 million euros in grant and loans each year.