On Wednesday, UN Special Envoy for Syria Staffan de Mistura decided to postpone the intra-Syrian talks in Geneva until February 25 as many preparatory issues, including humanitarian aid access to besieged areas in Syria, remained unresolved.
"I don't see [the suspension of Geneva talks] as a sit back in our day by day negotiations and efforts to get an access to besieged areas," O'Brien said.
The UN official stressed that safe access to those areas was vital.
"That is an international humanitarian law. It is not a question of negotiations. However, the best humanitarian relief can be provided when fighting is stopped. We all should support the resumption of talks in order to reach a political solution," O'Brien stressed.
As many as 400,000 Syrian civilians have been trapped in the besieged cities of Deir ez-Zur, Madaya, Foah and Kafraya for months, and they are suffering from severe malnutrition, according to the United Nations data.