Syrian peace talks cannot continue unless more humanitarian aid reaches civilians and the truce can only hold if rebels get more weapons, leading opposition envoy Riyad Hijab said Tuesday in Geneva.
Meanwhile, the death toll from government airstrikes on two towns in the north of the country increased to 44, according to a monitoring group and local activists.
The Syrian Observatory for Human Rights said 37 people were killed in Maarat al-Nuaman, on the country's main north-south highway south of Aleppo, and seven more in the nearby town of Kafr Nabl.
Local activists put the death toll between 45 and 50. Residents in the area told dpa that residential areas and street markets were hit by around 20 raids.
"It is not suitable to be in negotiations while people die in bombings, from hunger or under siege," Hijab said one day after his delegation announced it would pause its participation in the indirect talks with the Syrian government.
The government has been blocking aid convoys to areas besieged by its army in the past weeks, according to the United Nations.
"There is no cessation of hostilities on the ground because those that violate are not held accountable," Hijab added, pointing to alleged violations by the army and its military ally Russia.
In addition, Hijab demanded weapons for opposition rebels, as a condition for keeping the truce that has been in place since late February.
"To sustain the truce - it cannot be sustained by keeping the opposition from weapons," he told reporters.
"The regime is using the truce. They get weapons and munition and change balance," he added.
The Syrian army has been aided by Russia.
Arab Gulf countries and Turkey are thought to be the main weapons suppliers to opposition rebels, which are also backed by the United States.