Mr Alloush, from the High Negotiations Committee (HNC), said the talks had not brought a political deal or eased the plight of Syrians in besieged areas.
The HNC suspended its involvement in the UN-brokered "proximity" negotiations with a Syrian government delegation in Geneva in April.
No date has been set for a resumption.
"The three rounds of talks were unsuccessful because of the stubbornness of the regime and its continued bombardments and aggressions against the Syrian people," Mr Alloush said.
