Two Venezuelan government officials also told ABC News that Weddle was released and was being deported to the United States.
The syndicate said late Wednesday afternoon that Weddle and Camacho were being interrogated in the headquarters of Venezuela's Directorate General of Military Counterintelligence.
Camacho was released after about 12 hours, union officials said late on Wednesday.
Weddle, a freelance reporter based in Caracas, has contributed reporting to a number of news organizations, including ABC News.
“We’re deeply concerned by reports Cody Weddle and his colleague have been detained in Venezuela, and we urge the Venezuelan government to ensure their safety and to release them immediately," an ABC News spokesperson said in a statement.
Kimberly Breier, the United States' Assistant Secretary of State for Western Hemisphere Affairs, tweeted that the State Department was "aware of and deeply concerned with reports that another U.S. journalist has been detained" in Venezuela.
"We demand the journalist’s immediate release, unharmed," Breier added.
"Being a journalist is not a crime; the world is watching," a State Department spokesperson told ABC News.
With Wednesday's arrests, the number of journalists and press workers imprisoned this year rose to 36, officials with the Venezuelan press union said.
ABC News' Aicha El Hammar Castano contributed to this report.