Hundreds of Syrians fled the northern city of Maarat al-Numan Wednesday ahead of a feared military assault, as Turkey's prime minister pushed President Bashar al-Assad to end a crackdown against a widening anti-government uprising.

Witnesses and activists in Maarat al-Numan say Syrian troops intermittently shelled areas near the city and raided nearby villages, making arrests.

Major General Riad Haddad, head of the Syrian military's political department, said Wednesday that tanks surrounding the city had not “yet” entered – suggesting they were readying an operation. Syrian forces remain in control of the nearby flashpoint town of Jisr al-Shughour after pushing into it on Sunday.

General Haddad confirmed witness accounts that army units have also surrounded the eastern town of al-Boukamal near the Iraqi border, where clashes have broken out between protesters and pro-Assad loyalists.

The area borders Iraq's Sunni heartland and the two sides are linked by numerous family ties and trade routes. Forces also entered nearby Deir al-Zour, one of Syria's largest cities, where protests continued.

Meanwhile, Turkish Prime Minister Recep Tayyip Erdogan held crisis talks Wednesday with an envoy of Syria's president in Ankara. Hassan Turkmani met for almost three hours with Mr. Erdogan, who has expressed impatience over Syria's repressive tactics and slowness to reform, as well as anger over a growing humanitarian crisis.

No statements came out of the meeting.

The number of Syrians who have fled the violence and crossed the Turkish border in the past week has swelled to 8,500.

Turkish Foreign Minister Ahmet Davutoglu toured an area near the frontier Wednesday, stopping at the border fence to greet displaced people on the Syrian side. Davutoglu also spoke with wounded refugees lying on beds in Turkish camps.

Syria is urging people who fled to Turkey to escape the crackdown in Jisr al-Shughour to return home. Information Minister Adnan Mahmoud said electricity, water and communications had been restored to the city and that the area was safe.

An Associated Press reporter on a government-organized trip to Jisr al-Shughour was shown a mass grave there Wednesday, an attempt to bolster official claims that “armed gunmen” last week killed 120 security personnel.

But residents and soldiers who have deserted said those killed were civilians and security forces who had mutinied, refusing to shoot protesters and joining anti-government demonstrators.

In Geneva, the United Nations' top human rights official called for a thorough investigation into allegations of widespread abuses in Syria during the government's crackdown on dissent.

High Commissioner for Human Rights Navi Pillay also renewed her call Wednesday for Syria to grant access for a U.N. fact-finding mission. Her office has released a report citing allegations against Syrian forces that include an excessive use of force against civilians, arbitrary detentions and torture.

It says the most “egregious” allegations concern the use of live ammunition against civilians.

Rights activists say 1,300 civilians and 340 security force members have been killed since the protests against Mr. Assad's government began in mid-March.

About 10,000 people have been detained.