A second round of Syrian peace talks started acrimoniously Monday as the two sides traded accusations over disruptions to humanitarian operations in the city of Homs and the Syrian government alleged mass killings in nearby Hama.

The government accused Islamist rebel battalions of a “massacre” in a village in central Hama province, making for a tense beginning to the negotiations in Geneva.

Meanwhile, aid operations in Homs, planned as a measure to build confidence between the government and the opposition in initial talks last month, have been plagued by violence, with each side blaming the other for violations of a supposed cease-fire.

The shelling and gunfire targeting humanitarian workers attempting to reach rebel-held areas of Homs are reminders of the complexities of obtaining even the smallest concessions in a civil war in which developments on the ground have consistently outpaced diplomacy. Battle lines are constantly shifting; on Monday, the al-Qaeda-inspired Islamic State of Iraq and Syria (ISIS) withdrew from its bases in oil-rich Deir al-Zour after rebel infighting.

The two sides did not meet in Geneva on Monday, with U.N. mediator Lakhdar Brahimi instead holding separate sessions with each delegation. With tensions high, there are no plans for the two sides to sit in the same room Tuesday, either.

Opposition spokesman Louay al-Safi squarely charged the government with the attacks on aid workers in Homs and the deaths of at least three civilians.

“The negotiations cannot continue while the regime is stepping up its violence against the Syrian people,” he told reporters after his meeting with Brahimi.

The government, meanwhile, blamed “terrorists” for the disruption.

“How can we shoot at ourselves?” said Deputy Foreign Minister Faisal Mekdad. “This is ridiculous.”

Still, the supposed cease-fire was extended for three more days on Monday, and more than 460 civilians were evacuated, according to Syrian officials, bringing the total evacuated since Friday to more than 1,000.

There are disagreements over the agenda of the Geneva meeting, with the Syrian government insisting that talks focus on ending terrorism, while the opposition is eager to move on to the core issue of political transition. Matters including prisoner exchange and humanitarian access are likely to be discussed on the sidelines, diplomats said.

“If terrorism does not stop in Syria, it will spread to neighboring countries and all the countries of the world,” Mekdad told reporters in Geneva on Monday. “This is the main menace to peace in Syria.”

Syria said it had submitted to the United Nations a draft statement condemning killings in the pro-government village of Maan in Hama, largely home to Alawites, members of the same sect as President Bashar al-Assad. It requested “an immediate and very clear condemnation” from Brahimi.

Syrian state news agency SANA said the dead included 42 women, children and elderly people.

The Islamist brigades Ahrar al-Sham and Jund al-Aqsa were among the rebel groups that claimed to have “liberated” the village. Videos posted online showed rebels pulling down the state flag. One showed a slain man in military fatigues.

The Syrian Observatory for Human Rights said 25 people were killed, mostly fighters with the National Defense Force, a pro-government paramilitary group.

Western diplomats are pressing for more rebel groups to engage with the Geneva process, amid questions about the point of talks with an external opposition that has little power over the fighters within Syria.

Rebels are also wracked by infighting as they attempt to oust fighters from ISIS, which even al-Qaeda has disowned.

Al-Qaeda’s local affiliate, Jabhat al-Nusra, was among the rebel groups that expelled ISIS from Deir al-Zour, an indication of ISIS’s growing isolation. In a statement Sunday, ISIS accused Jabhat al-Nusra of having “stepped away from the road of the righteous.” The Syrian Observatory said ISIS had pulled out after Jabhat al-Nusra refused its requests for mediation.

Ahmed Ramadan in Beirut contributed to this report.