The number of detentions from mass demonstrations in Venezuela previously stood at 850 people.
"700 people remain in custody from January 21. A total of 966 have been detained," Romero wrote on Twitter.
The situation in Venezuela, which has been struggling to overcome a political crisis amid the opposition's refusal to recognize last year’s re-election of President Nicolas Maduro, significantly escalated on January 21 when the opposition-controlled National Assembly declared the president an usurper.
Maduro called the opposition leader Juan Guaido a US officials' puppet and accused Washington of attempting to organize a coup in Venezuela, declaring the decision to cut off diplomatic ties with the country.
READ MORE: Maduro Calls Lima Group's Declaration on Venezuelan Crisis 'Ridiculous'
Canada, the United States and many of their allies have recognized Guaido as interim president of Venezuela. Russia, China, Turkey and other countries regard Maduro and his government as legitimate authorities in Venezuela.