UNITED NATIONS / BEIRUT / ANKARA: A human rights group accused the Syrian government Monday of conducting at least eight chemical attacks using chlorine gas on opposition-controlled residential areas during the final months of the battle for Aleppo. Meanwhile, Syrian rebels cast doubt that they would attend Russian-backed peace talks in Kazakhstan this week, accusing Moscow of failing to get Damascus to fully comply with a cease-fire deal or release any prisoners.

Human Rights Watch said in a report released Monday that it used witness interviews and video footage to document government helicopters carrying out the attacks in rebel-held eastern Aleppo that killed at least nine civilians, including four children, and injured around 200 people.

The attacks took place in areas where government forces were planning to advance, following the front lines as they moved from east to west, the rights group said.

Ole Solvang, the organization’s deputy emergencies director, said: “The pattern of the chlorine attacks shows that they were coordinated with the overall military strategy for retaking Aleppo, not the work of a few rogue elements.”

The Syrian government has previously denied any chemical attacks.

Human Rights Watch said the attacks were carried out between Nov. 17 and Dec. 13 – two days before President Bashar Assad’s forces took control of eastern Aleppo in a humiliating defeat for opposition fighters trying to oust the Syrian leader.

Rebel officials said Monday that they would not be attending peace talks in Kazakhstan set for Feb. 15-16 in preparation for U.N.-backed talks in Geneva Feb. 23.

“There were violations in the cease-fire and the Russians did not live up to their promises to halt these violations,” Mohammad al-Aboud, a senior rebel official, told Reuters.

A second rebel official, speaking on condition of anonymity, said at most a handful of rebels might attend, but only if progress was seen in the next two days. “The [whole] delegation will not go,” he said.

The Syrian government said earlier Monday it was ready to agree on prisoner swaps with rebel groups, a potential confidence-building measure as the United Nations prepares to convene new peace talks. The Syrian opposition has long demanded the release of government-held detainees as one of several humanitarian actions needed before any negotiations over Syria’s political future.

The government was “always ready” to exchange prisoners in its jails for people “kidnapped by terrorist groups,” Syrian state media cited an official source as saying.

A rebel official dismissed the statement as a ruse, saying Damascus had far more detainees than the few the rebels held.

U.N. envoy Staffan de Mistura’s office said he was “actively engaged” in diplomatic efforts aimed at bringing Syrian government and opposition delegations back to Geneva for the first time since the talks were suspended amid an upsurge in fighting last April.

De Mistura had previously said the talks were expected to resume on Feb. 20 but his office said now the delegations would first hold preliminary meetings with de Mistura’s team in the Swiss city.

On the ground, Syrian militants seen as close to Daesh (ISIS) battled a rival hard-line Islamist faction Monday in northwestern Syria, an activist group and an official with another insurgent group said.

Jund al-Aqsa and Tahrir al-Sham clashed around Kafr Zeita in the countryside north of Hama, and near Tamanaa, Khan Sheikhoun and Tal Aaas in southern Idlib Province, said the Syrian Observatory for Human Rights, a Britain-based group of activists on gthe ground.

An official with a rebel group that fights under the banner of the Free Syrian Army, which was not involved in Monday’s confrontations, confirmed the fighting.

A statement released by Tahrir al-Sham said Jund al-Aqsa was responsible for the violence, accusing it of coordinating with Daesh and of having attacked Tahrir al-Sham with suicide blasts and a car bomb.

In other developments, President Recep Tayyip Erdogan said that Ankara wanted to establish a “safe zone” in northern Syria free of “terrorists,” as Turkish-backed rebels pushed ahead in the town of Al-Bab.

He added the area would also require a “no-fly” zone.

“Our objective here is [to establish] an area of at least 4,000, 5,000 square kilometers free from terrorism, to create a safe zone,” Erdogan said in a televised speech in Bahrain.

Turkey has repeatedly called for such a zone, which it believes could help to alleviate the burden of accommodating Syrian refugees.

Also Monday, authorities in the central Syrian city of Hama unveiled a statue of late President Hafez Assad to replace the one pulled down by demonstrators nearly six years ago, in the early days of the uprising against his son’s rule.

The new statue stands on the same spot where the earlier one stood. Hafez Assad ruled Syria for 30 years before Parliament passed power to his son, in 2000. He besieged Hama in response to a revolt by the Muslim Brotherhood in 1982. An estimated 10,000 to 40,000 people were killed at the time.

In southern Syria, fresh clashes between the government and rebels in the contested Deraa province killed at least 23 people, according to the Observatory. The fighting punctured an otherwise prolonged period of relative calm between the two sides.