Opposition activists said thousands of Syrians had fled their homes as the government troops executed a major offensive in Deir Ezzor just a day after U.N. Secretary-General Ban Ki-moon called President Bashar Assad and urged him to halt the use of force against civilians.
Ban's request apparently went unheeded.
"The city has never witnessed a day like this," an opposition spokesman told The New York Times by phone as bursts of gunfire were heard in the background.
Another opposition leader told CNN loud explosions could be heard around town.
Turkish daily Sunday's Zaman said Foreign Minister Ahmet Davutoglu planned to visit Syria and convey a stern message to authorities. "We have been very patient until now, waiting to see whether we can fix this, whether they will listen to what we have been saying. But our patience has run out," Prime Minister Recep Tayyip Erdogan said Saturday.
Voice of America reported activists said at least 55 people had been killed throughout the country Sunday, with Haytham Manna, spokesman for the Arab Commission for Human Rights, saying violence had also broken out in Houleh in Homs province and other cities. The U.S. broadcaster said the casualty reports had not been confirmed independently by journalists, who are barred from the region by the government.