The UN’s peace envoy to Syria, Staffan de Mistura, said Sunday he would visit Damascus soon while renewing his criticism of the use of barrel bombs by President Bashar Al-Assad’s regime, AFP reports.

Without specifying when the visit would be, de Mistura’s spokesman the envoy “intends to raise with the Syrian Government the issue of protection of civilians, underlining once again the unacceptable use of barrel bombs”.

He called on the government to respect international law and to honor its “incontestable duty” to protect civilians.

The United States, Britain, France and rights groups have accused Assad’s forces of using barrel bombs — crude weapons made of containers packed with explosives that are dropped from helicopters.  

On May 30, at least 45 civilians were killed and dozens more wounded in a barrel bomb attack in the northern province of Aleppo, according to the Syrian Observatory for Human Rights, a Britain-based monitoring group.

De Mistura previously called the civilian deaths in barrel bomb attacks “totally unacceptable”. Assad, however, has repeatedly denied using barrel bombs and has suggested in interviews that no such weaponry exists.

The envoy’s announcement came after he said on Wednesday he was extending wide-ranging talks in Geneva by another month until July.

The talks were launched May 5 to allow separate consultations with regional and domestic players in the hope of reviving dialogue on the four-year conflict.

“Mr. de Mistura looks forward to meeting with senior Syrian officials with the aim of giving them the opportunity to express their own views around the Geneva Consultations,” the statement said, adding that the envoy had “decided to respond positively to an invitation” from the government in Damascus.

The envoy “also plans to discuss the current humanitarian situation in Syria and ways to increase access to besieged and conflict-affected communities”.