The Syrian army launched more raids on protest strongholds today, defying growing international criticism over the regime's deadly crackdown.
Turkey's foreign minister met President Bashar Assad to express his concern.
Envoys from India, Brazil and South Africa also headed to Damascus to press for an end to the bloodshed, which activists say has killed about 1,700 people since March.
The visit by Turkish Foreign Minister Ahmet Davutoglu is significant because Turkey until recently had close ties to Damascus. But Ankara has become increasingly critical of its neighbour over the bloodshed.
Activists said tanks stormed villages outside the besieged city of Hama and two towns in Idlib province, which borders Turkey. There was heavy machine-gun fire in the eastern city of Deir el-Zour, which also has been a flashpoint in recent days.
India's UN Ambassador Hardeep Singh Puri said his country's representative will join those from Brazil and South Africa for a meeting with Syria's foreign minister to appeal for an end to the crackdown and to promote democratic reforms.
The Syrian regime has shown no signs of scaling back its crackdown despite Damascus' increasing diplomatic isolation. Saudi Arabia, along with Bahrain and Kuwait in the Gulf, recalled their ambassadors this week.
The latest wave of bloodshed started a week ago, on the eve of the Muslim holy month of Ramadan, when tanks and snipers laid siege to Hama, which had largely freed itself from government control earlier this year.
Residents were left cowering in their homes, too terrified to peek through the windows. The city is haunted by memories of the regime's tactics: In 1982, Assad's father and predecessor, Hafez, ordered the military to quell a rebellion by Syrian members of the conservative Muslim Brotherhood movement there, sealing off the city in an assault that killed between 10,000 and 25,000 people.
Since the start of Ramadan, more than 300 people have been killed in cities including Hama and Deir el-Zour, an oil-rich but largely impoverished region known for its well-armed clans and tribes whose ties extend across eastern Syria and into Iraq.