Turkish Foreign Minister Ahmet Davutoglu is going to Syria to demand an end to a crackdown on protests by President Bashar al-Assad’s government.
Turkish PM Recep Tayyip Erdogan earlier said he was running out of patience over “the savagery” of Syria’s security forces towards the protesters.
Mr Davutoglu’s visit comes as Saudi Arabia, Kuwait and Bahrain have all recalled their ambassadors to Damascus.
Syrian tanks again pounded the eastern city of Deir al-Zour on Monday.
At least 50 people died on Sunday after the army launched a pre-dawn assault.
Activists said that as in recent days, many people had been afraid to leave their homes or take injured people to hospital for fear of being attacked.
Syrian state TV has reported that Mr Assad has appointed a new minister of defence, former army chief of staff Gen Dawoud Rajha. He replaces Gen Ali Habib, said the report.
Sana has also said troops are withdrawing from the city of Hama, which has come under heavy attack in recent days – witnesses say scores of people have died there.
Access to Syria has been severely restricted for international journalists and it is rarely possible to verify accounts by witnesses and activists.
Human rights activists say at least 1,700 civilians have been killed and tens of thousands arrested since the uprising began in mid-March. More than 300 people are believed to have died in the past week alone.
On Tuesday, Mr Davutoglu, the architect of Turkey’s outreach to its Arab neighbours, will be making a last-ditch effort to persuade President Assad to change course, the BBC’s Jonathan Head in Istanbul reports.
Mr Davutoglu may threaten Turkish support for stronger action by the UN Security Council, although few believe he will have much success, our correspondent says.
President Assad’s spokeswoman has already warned of an equally tough reply from Damascus.
Turkey’s Muslim constituents sympathise with protesters in the neighbouring country who have also drawn inspiration from Islam, and there is outrage here over the attacks that have continued into the holy month of Ramadan, our correspondent says.
But he says that there is no suggestion yet that Ankara will downgrade its diplomatic ties. It is also opposed in principle to economic sanctions, which, if implemented by Turkey, really could hurt the Syrian government.
In a statement over the weekend, King Abdullah of Saudi Arabia said the events in Syria were “unacceptable”, and that Damascus had to choose between “wisdom” or being “pulled down into the depths of chaos and loss”.
The BBC’s Jim Muir in Beirut says that by Arab diplomatic standards, it was a highly dramatic intervention by the Saudi monarch, one of the most influential powers in the region.
King Abdullah said he had recalled his ambassador from Damascus for consultation. That move was followed by Kuwait and then Bahrain.
On Monday the Arab League’s head, Nabil al-Arabi, said he hoped the crisis could be overcome “by peaceful means and by launching a serious dialogue towards the reconciliation that the people have been demanding”.
Meanwhile the top Sunni Muslim authority, Cairo-based al-Azhar, said the situation in Syria had “gone too far”.
The US State Department has said it is “very much encouraged by the strong statements” from the region.
Damascus says it is tackling “armed terrorist gangs” and that its critics have ignored its promises of political reform.