"We claim that Carlos Graffe, the head of Voluntad Popular in Carabobo [state] was kidnapped. They will not manage to prevent July 16 referendum," Freddy Guevara said on Twitter.
According to the information of the opposition, Graffe was detained by Venezuelan intelligence servicemen in the city of Valencia. His location is unknown.
The opposition has scheduled a referendum for July 16, which will question the legitimacy of constitutional assembly proposed by President Nicolas Maduro and the need for the elections in Venezuela.
Venezuela has been facing anti-government protests amid an economic crisis in the country. The recent wave of protests started in April as a result of the decision of the Supreme Court to take on functions of the country's parliament controlled by opposition.
In May, Maduro said he was going to convene a special assembly with a power to rewrite the constitution as a way out of the deepening political crisis that gripped the country in early April after the Supreme Court’s attempt to curb parliamentary powers.