Marco Ruiz, the union’s president, said that according to the witnesses, the pair were accused of two crimes – espionage and treason.
US senators Marco Rubio and Rick Scott of Florida expressed outrage at the detention, Mr Scott saying the US would “not stand for this intimidation”.
The director of the US-based Human Rights Watch, Jose Miguel Vivanco, said it was “very worrying”, adding that the “desperate regime” of Mr Maduro was doing “the only thing it knows how to do: repress and censor”.
Luis Almagro, secretary-general of the Organisation of American States, castigated the “oppressive usurper regime of Venezuela”, calling for an “end to the intimidation and censorship” of journalists in the country.
Venezuelan security forces have detained 49 reporters, some of them briefly, so far this year, according to Espacio Publico, a press monitoring organisation.
The group is investigating the circumstances of Weddle’s detention but had yet to receive any explanation from authorities, a representative told The Telegraph.