UN Syria envoy Staffan de Mistura voiced "horror and outrage" at the attacks claimed by the Islamic State group that killed around 35 people in the Belgian capital Tuesday.
"The tragedy in Brussels ... Reminds us that ... We have no time to lose," UN Syria envoy Staffan de Mistura told reporters in Geneva.
"We need to extinguish the fire of war in Syria," he said, insisting that "to fight terrorism, the best formula is to find a solution for political transition in Syria."
HNC spokeswoman Bassma Kodmani said the UN-brokered Syrian peace talks were "more vital than ever".
"The Geneva process is today fundamental to reestablishing the global political order and avoiding the chaos that fanatics are threatening us with here in Europe and there in the Middle East," she said in a statement.
But despite the calls to speed up the process, the Geneva talks, which are in their second week, remain indirect and continue to move at a snail's pace.
The envoy, who has been shuttling between the two sides, said today he is eager to make progress before the negotiations pause on Thursday, telling reporters: "We are all working hard on getting a common understanding."
But the talks continue to stumble on the fate of Syrian President Bashar al-Assad, with the regime's lead negotiator in Geneva, Bashar al-Jaafari on Monday reiterating that discussing the issue was "excluded."
Assad's fate has been a key obstacle in the latest talks aimed at ending Syria's devastating five-year war, which has killed more than 270,000 people and displaced millions.
France-based Middle-East expert Agnes Levallois told AFP the regime was dragging its feet in the talks, "because when real negotiations begin, it will be the beginning of the end.
