The Arab League has sent an "urgent message" to the Syrian government, denouncing "the continued killings of civilians" taking part in protests.
The League's ministerial committee on the Syrian crisis also urged Damascus to "take the necessary measures" to protect civilians.
The call came as at least 37 protesters were killed in Syria, activists said.
The deaths took place mostly in Homs and Hama as protesters called for a no-fly-zone to be imposed, activists said.
More than 3,000 people have died in the unrest since protests broke out in March.
The government of President Bashar al-Assad says the unrest is being stoked by armed gangs and foreign extremists looking to stir up sectarian strife.
Foreign journalists have been largely prevented from reporting from the country, making it difficult to confirm events on the ground.
The Arab League's committee on Syria issued its statement on Friday.
It said that the committee would meet Syrian officials on Sunday in Qatar to try to reach "serious results" on a way to end the crisis.
The ministers also said that they had held "frank and friendly" talks with President Assad on Wednesday.
Earlier on Friday, protesters in Syria called for international protection from Nato whose war planes played a vital role in the overthrow of former Libyan leader Muammar Gaddafi.
"God, Syria, we want a no-fly zone over it," protesters shouted in the Bab Tadmur neighbourhood of Homs, while others carried banners demanding international protection, Reuters reports.
In the restive Balaa neighbourhood, around 20,000 people marched calling for the fall of President Assad's regime, Agence France-Presse reports, quoting the London-based Syrian Observatory for Human Rights.
An armed insurgency has emerged over the past few weeks around the city, home to one million people and some 140km (85 miles) north of Damascus, the news agency reports.
Dozens of young protesters marched in Damascus' Barzeh neighbourhood, the Observatory said, adding that 40 were arrested.
Internet and communications services were reportedly disrupted in parts of the capital, as well as in Homs.
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