Security forces have killed at least 44 people across Syria following Friday prayers, according to the Syrian Revolution General Commission, an opposition group.
Clashes between security forces and protesters erupted mainly in the Idlib province, the outskirts of Homs, and in the Damascus suburb of Doumma, pro-democracy activists said.
In the city of Hama itself, security agents "surrounded the Saad bin Abi Waqas mosque" anticipating a protest after Friday prayers, activists said.
Citing activists on the ground, the Syrian Observatory for Human Rights, a UK-based group, reported several tanks and troop transports heading towards the northwest town of Maaret al-Numan in Idlib province.
Elsewhere, communications were cut on Friday in Zabadani, about 50km northwest of Damascus.
The latest deaths came after Ban Ki-moon, the UN chief, called for "coherent" global action over President Bashar al-Assad's security crackdown on the pro-democracy movement.
'Enough is enough'
In comments made on Thursday, Ban said: "When [Assad] has not been keeping his promises, enough is enough and the international community should really take coherent measures and speak in one voice."
Recep Tayyip Erdogan, the Turkish prime minister, who was visiting Libya on Friday on the final leg of an Arab Spring tour, also criticised Assad, telling him the era of oppressive dictators is past.
Speaking 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".
Erdogan is expected in New York next week, and the White House said Barack Obama would discuss with him the crisis in Syria and wider turmoil in the Middle East.
Ben Rhodes, the US president's deputy national security adviser, 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.
In-depth coverage of escalating violence across Syria
"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," Beatrice Megevand-Roggo, the International Committee of the Red Cross' operations head in the region, said.
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.
"A merciless attack on a Red Crescent ambulance is the latest evidence of grave danger to humanitarian workers in the embattled Syrian city of Homs," Human Rights Watch, the New York-based rights watchdog, said,
Opposition protesters had called for more rallies on Friday, undaunted by the crackdown the UN says has killed more than 2,600 people.
"This Friday the protest enters it seventh month," Al Jazeera's Omar al-Saleh reported from Amman, the Jordanian capital.
According to the Local Co-ordination Committee, an opposition group, since the beginning of the uprising 761 people have been killed in Homs, 594 in Deraa, and 350 in Hama.
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 the Facebook page The Syrian Revolution 2011.