Dozens of people have been killed by security forces in Syria amid nationwide protests in support of the flashpoint city of Hama on the first Friday of Ramadan, the Muslim fasting month, reports say.
The Local Co-ordination Committees of Syria, an activist organisation in the country, said 24 people had been killed across several cities.
Security forces fired at demonstrators in Irbin, near Damascus, killing five people and wounding many others, Abdel Karim Rihawi, head of the Syrian League for the Defence of Human Rights, an opposition group, told the AFP news agency in Nicosia, Cyprus.
"Thousands of demonstrators marched in Deir ez-Zor, Deraa and Qamishli in support of the city of Hama despite the extreme heat," he said.
He said they numbered 30,000 in Deir ez-Zor alone.
Another Syrian activist, Rami Abdel Rahman, said 20 people were wounded, seven of them seriously, when security forces opened fire in the Ter Maala district of the central city of Homs.
Abdel Rahman said that "more than 12,000 people" marched in Bench, in the northern Idlib province, "to demand the fall of the regime and express their support for Hama and Deir ez-Zor".
"Hundreds of people came out of the al-Mansuri mosque in Jablah, chanting 'God is with us'," he said, referring to a city on Syria's Mediterranean coast.
It is difficult to verify independently reports of the deaths as the Syrian authorities refuse to allow the media into the country.
State television said two members of the security forces were shot and wounded by armed men posted on rooftops in Douma, a suburb of Damascus.
Pro-democracy activists say communications have been completely cut off as the army steps up an operation to crush dissent in Hama, 200km north of Damascus, where security forces reportedly killed at least 30 civilians and wounded dozens more earlier in the week.
The call for Friday's solidarity protests came from activists on the Facebook group, The Syrian Revolution 2011, a driving force behind the demonstrations calling for greater freedoms in the country since mid-March.
Rights activists say Bashar al-Assad, the country's president, has sought to crush the democracy movement with force, killing more than 1,600 civilians and arresting thousands of dissenters.
Its latest crackdown has centred on Hama, where at least 45 people were killed on Wednesday by tanks shelling the city centre.
The city was isolated on Friday, and the military continued an operation to combat what Assad's government calls "armed terrorist gangs" responsible for the deadly unrest.
State media reported that army units were removing "roadblocks set up by terrorist groups that have blocked roads and damaged public and private property, including police stations, using various weapons."
In-depth coverage of escalating violence across Syria
The crackdown on Hama has prompted harsh US criticism, with even Russia hinting at a possible change of heart after resisting firm UN action against Syria, its ally since Soviet times.
The White House said the deadly crackdown had put Syria and the Middle East on a "very dangerous path", as the US expanded its sanctions to include a businessman close to al-Assad and his family.
It has frozen the US assets of Mohammad Hamsho and his company, Hamsho International Group, and prohibited US entities from engaging in any business dealings with them.
The US, French and German leaders pledged to consider new steps to punish Syria.
Obama spoke separately to France's Nicolas Sarkozy and German Chancellor Angela Merkel as Western nations cranked up pressure on Assad.
"The leaders condemned the Assad regime's continued use of indiscriminate violence against the Syrian people," a White House statement said Friday.
"They welcomed the August 3 presidential statement by the UN Security Council condemning Syria's actions, but also agreed to consider additional steps to pressure the Assad regime and support the Syrian people."
The telephone consultations came as Washington appeared to be moving towards a direct call for Assad to leave, after saying this week his presence was now fomenting instability and leading the Middle East down a dangerous path.
Pro-democracy activists have dismissed as a ploy a new law allowing the creation of political parties alongside the Baath party, as decreed by Assad on Thursday.
The decree came after the UN Security Council condemned the crackdown and said those responsible should be held accountable, in a non-binding statement rather than a resolution.