Security forces in Syria shot dead at least 22 people in operations across the country on Friday, the Syrian Observatory for Human Rights said, as pressure mounted on the regime to end the crackdown.
The latest deaths came after UN chief Ban Ki-moon called for "coherent" global action over President Bashar al-Assad's deadly response to dissent, as dissidents marked six months of anti-regime protests in Syria.
And Turkish Prime Minister Recep Tayyip Erdogan, in Libya on the final leg of an "Arab Spring" tour, lashed out at Assad, telling him the era of oppressive dictators is past.
Erdogan is expected in New York next week, and the White House said President Barack Obama would discuss with him the crisis in Syria and wider turmoil in the Middle East.
Four people were shot dead by security forces in Damascus and its environs, nine in the central cities of Hama and Homs, six in southern Daraa province and three in Idlib, the Britain-based Observatory told AFP.
Another 15 bodies had been discovered in various cities, said the Observatory, adding most had been killed in the past 24 hours.
State television said one member of the security forces was killed and another four were wounded at Basr al-Harir in southern Daraa province during an attack by "armed groups."
In the city of Hama itself, security agents "surrounded the Saad bin Abi Waqas mosque" anticipating a protest after Friday prayers, activists reported.
In July, Hama saw protests by hundreds of thousands of people calling for the downfall of Assad's regime, but the rallies were put down by security forces using deadly violence.
Citing activists on the ground, the Observatory also reported several tanks and troop transports bearing down on the northwest town of Maaret al-Numan in Idlib province.
Elsewhere, communications were still cut on Friday in Zabadani some 50 kilometres (30 miles) northwest of Damascus, where one man has been reported killed and 153 people arrested since Tuesday.
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Opposition protesters had called for more rallies on Friday, the Muslim day of weekly prayer when demonstrations tend to be the heaviest, undaunted by the crackdown the United Nations says has killed more than 2,600 people.
The rallies were staged under the slogan "we advance toward the fall of the regime."
"Six months. More than ever determined to (continue) the March 15 uprising," activists wrote on Facebook page The Syrian Revolution 2011, one of the main engines of the revolt.
Ban said on Thursday of Assad that "when he has not been keeping his promises, enough is enough and the international community should really take coherent measures and speak in one voice."
The UN chief has had several telephone conversations with Assad since the protests erupted on March 15, during which the president repeatedly promised to end the bloody crackdown and institute political reforms.
In Tripoli, Erdogan said "those who oppress the people of Syria... should understand that his time is is past because the era of repressive regimes has ended."
A Turkish daily quoted him as saying Ankara has warned Iran "not to spoil" the Syrian leadership by encouraging Damascus in its crackdown on dissent.
Erdogan said he had discussed the matter with President Mahmoud Ahmadinejad of Iran, which accuses its arch-foes Israel and the United States of stirring up trouble in Syria.
In Washington, deputy national security adviser Ben Rhodes said he expected Obama and Erdogan "will talk about events in Syria where we share great concerns with the Turks about the actions of President Assad."
"We have a very close, broad, alliance and working relationship with Turkey," Rhodes said.
The Red Cross, meanwhile, condemned attacks on medical services in Syria, saying relief workers and ambulances have come under fire on several occasions.
"It is completely unacceptable that volunteers who are helping to save other people's lives end up losing their own," said Beatrice Megevand-Roggo, the International Committee of the Red Cross' operations head in the region.
A Syrian Arab Red Crescent volunteer died this week from his injuries and two others were hurt after their ambulance was caught in heavy fire while transporting a wounded person, said the relief agency.