Humanitarian workers braved mortar shells and gunfire Sunday as they pushed forward with their mission to deliver aid into besieged parts of the Syrian city of Homs and evacuate citizens, a day ahead of peace talks between the two sides.

The three-day “humanitarian pause” that started Friday to allow civilians out of Old City Homs — and allow aid in — was blighted by violence. Despite incessant explosions, more than 600 civilians were evacuated Sunday, according to Syrian officials and rebels.

The Syrian government has been under pressure from allies Russia and Iran to allow aid into the besieged areas of Homs to show willingness ahead of the second round of peace talks in Geneva, which begin Monday.

But the cease-fire has been far from simple. For the evacuees, the journey out was a perilous one. Rebels said that at least six people died Sunday under mortar fire as they gathered to leave in the al-Qarabees neighborhood of Homs.

But the desperate situation inside meant many risked the journey. The area has been under a stranglehold from government forces for more than 18 months, with food in short supply.

A total of 611 evacuees joined the 83 who left Friday, Homs Gov. Talal Barazi told the Syrian state news agency SANA . Some men between the ages of 16 and 54 who had been told not to leave negotiated their exit after agreeing they would “face responsibility” if they are wanted for a crime, he said, adding that a plan to extend the truce to allow more evacuations was under discussion.

Rebels confirmed that around 600 people left the city.

Because of the mortar fire Sunday, trucks carrying food were unable to enter the besieged areas. Some limited supplies of food were brought in SUVs, activists and aid workers said.

The United Nations delivered 250 food parcels and 190 hygiene kits into the Old City on Sunday night, but the supplies had not been distributed.

The delivery made it through despite the convoy coming under direct fire.

“The quantity is just not enough,” said Waleed al-Fares, an activist based in the city. “We are waiting to know if more will arrive before we decide how to distribute.”

Before evacuations began, the United Nations estimated that 2,500 civilians were trapped in the Old City, but Fares said the number was closer to 3,000, plus thousands of fighters.

Syrian government officials have balked at delivering aid in the past, saying they did not want it to fall into the hands of “terrorists.”

Both sides have blamed each other for the breach in the cease-fire, with rebels saying mortars were fired by militias loyal to President Bashar al-Assad. A video showed the trucks, escorted by white SUVs, driving through the war-ravaged streets, to the sound of loud explosions.

U.N. humanitarian chief Valerie Amos said she was “deeply disappointed” that aid workers had been targeted.

Humanitarian access will continue to be discussed on the sidelines of talks between the Syrian government and opposition in Geneva, although the talks are expected to focus on the core issue of political transition.