By Luc Cohen and Leon Wietfeld
CARACAS (Reuters) - A riot erupted on Wednesday at a detention center where dozens of government opponents of Venezuelan President Nicolas Maduro and a Mormon missionary from Utah are detained, activists and relatives said on Wednesday.
There was no official information on the incident and family members said they were in the dark about what was happening at the Helicoide, headquarters of intelligence agency Sebin, where several hundred people are behind bars.
The riot was sparked after a young activist from the mountainous state of Tachira, Gregory Sanabria, was beaten by other prisoners, according to Patricia Gutierrez, wife of detained opposition leader Daniel Ceballos.
That appeared to have sparked "some of sort of internal fight," said Alfredo Romero, a lawyer and activist with the Penal Forum rights group, speaking in front of the Helicoide.
In videos posted on social media, Venezuelan activists, including a man identified as Sanabria whose face was bruised, pleaded for help.
Joshua Holt, a U.S. citizen and Mormon missionary, posted on his Facebook page around 3:00 pm EST, "Helicoide the prison where I am at has fallen the guards are here and people are trying to break in my room and kill me. WHAT DO WE DO?" His mother Laurie Holt confirmed the account belonged to her son.
The U.S. embassy in Caracas said it was "very worried" about the situation.
"Joshua Holt and other U.S. citizens are in danger. The Venezuelan government is directly responsible for their security and we will hold them responsible if anything happens to them," the embassy tweeted in Spanish.
Reuters was not able to determine the situation inside the Helicoide.
Venezuela's Information Ministry did not respond to a request for comment. Venezuela's chief prosecutor said his office was on site, but did not provide details.
"In the face of the events that happened today in the Sebin headquarters at the Helicoide, we sent a commission of the prosecutor's office to the facility. That delegation spoke to a representative of the prisoners to respond to their requests," chief prosecutor Tarek Saab tweeted.
(Additional reporting by Alexandra Ulmer and Vivian Sequera; Editing by Toni Reinhold)