(CNN) -- U.N. Secretary-General Ban Ki-moon on Saturday called on Syrian President Bashar al-Assad to halt the use of force on civilians "immediately."
Ban spoke to the Syrian leader by phone to express "his strong concern and that of the international community at the mounting violence and death toll" in the country over the past week, according to a U.N. readout of the conversation.
The discussion took place after several days of raging violence in the country.
Anti-government protests erupted Friday across the country, but the turbulent city of Hama appeared to have borne the brunt of it.
The city endured steady shelling and bombing Friday morning while the government's military offensive continued in full swing, said a resident whom CNN is not naming for his safety.
Two witnesses, who talked to CNN independently, said scores of people -- one said he had counted 53; the other said 58 -- were killed instantly when a tank positioned 150 meters (164 yards) from Hurani Hospital launched an artillery shell that landed in front of the building. One opposition activist estimated that 300 people have died in violence in Hama during the past six days.
In his conversation with the U.N. leader, Al-Assad pointed to reform measures announced this week under international pressure to end the crackdown on peaceful protests. The measures include a decree authorizing a multiple-party political system.
Ban "underscored that for these measures to gain credibility, the use of force and mass arrests must stop immediately," the U.N. statement said.
Also Saturday, clashes continued in Idlib, Daraa and the Damascus suburb of Nahr Aysha, witnesses said. Heavy gunfire could be heard and Syrian security forces were working to disperse thousands of demonstrators who gathered in some areas after the day's prayers, the witnesses said.
In the northeastern city of Deir Ezzor, an opposition activist said security forces have entered the city with tanks and bulldozers. The movement early Sunday comes after a video was posted Friday on YouTube showing a man telling tribal leaders that he had received information that the army would conduct an operation there. The man is seen telling the men to prepare for a military assault.
The activist, who CNN is not identifying for safety reasons, said Deir Ezzor residents have installed barricades of poles and rocks in an attempt to block an assault.
Meanwhile, the country's foreign minister announced plans Saturday to hold parliamentary elections by the end of the year, the state-run news agency reported.
Walid Moallem told Arab and foreign ambassadors that the country's leadership is resolved to move ahead with reforms and provide free and fair elections for the country, the Syrian Arab News Agency reported.
He spoke in Damascus amid Syria's five-months-long political crisis. Thousands have taken to the streets since mid-March to demand a slew of political reforms and an end to the al-Assad regime.
The Syrian Observatory for Human Rights, an activist group, said 2,000 people have died in the unrest, mostly demonstrators.
Moallem said Syria is intent on fostering security, stopping vandalism, and pursuing democracy and progress, SANA reported.
CNN's Kamal Ghattas contributed to this report.