Syria's army launched assaults across the eastern city of Deir Ezzor on Sunday. Activists say explosions can be heard in several parts of the city.

The pre-dawn raid comes a day after U.N. Secretary-General Ban Ki-moon told Syrian President Bashar al-Assad to immediately stop using military force against civilians taking part in a four-month-old anti-government uprising.

The U.N. press office says Mr. Ban told the Syrian leader in a rare telephone call Saturday he has “strong concern” at the mounting violence and death toll in the Syrian uprising in recent days.

Mr. Ban's office says he also told Mr. Assad that political reforms promised by the president can become credible only if there is an immediate end to the use of force and mass arrests against opposition activists. Syria had no immediate comment on the phone conversation.

In the latest government gesture to the protesters, Syrian Foreign Minister Walid Moallem said Saturday authorities will hold free parliamentary elections by the end of this year. Opposition activists have dismissed such gestures in the past.

The United States says Mr. Assad's security forces have killed about 2,000 people since the uprising began in March.

Other international leaders and governments also increased pressure on Mr. Assad to stop the crackdown.

Turkish Prime Minister Recep Tayyip Erdogan said his government has reached “the end of our patience” with Syria, Turkey's southern neighbor. He said Turkish Foreign Minister Ahmet Davutoglu will visit Syria Tuesday to deliver that message in a firm manner. Ankara had close ties with Damascus in the years before the revolt began.

In another warning to Syria, German Foreign Minister Guido Westerwelle told a German newspaper that he does not believe Mr. Assad has a political future that the Syrian people will support.

Gulf Arab states also broke their silence about the uprising. The six-nation Gulf Cooperation Council issued a statement calling for an immediate end to the violence and for the implementation of reforms. The bloc includes Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates.