Geneva -- The U.N. human rights office has said security forces in Venezuela detained nearly 700 people in one day last week amid anti-government protests -- the highest such tally in a single day in the country in at least 20 years. Rights office spokesman Rupert Colville said Tuesday that 696 people were detained on Wednesday alone. Overall, some 850 were detained between Monday and Saturday, including 77 children.

Colville said "more than 40 people" were believed to have been in killed "in different manners" amid the recent protests, including 11 people reportedly killed by "unidentified individuals" linked to incidents of looting. He said one member of the Bolivarian Guard was reportedly killed in the state of Monagas.

He told reporters in Geneva that officials were investigating reports of ill-treatment of detainees.

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The violence and arrests in the once-rich South American nation have continued unabated since opposition leader and Juan Guaidó declared himself interim president of Venezuela last week -- a move backed early by the Trump administration, and since by a large number of other democracies around the world.

The U.S. and its allies consider current Venezuelan President Nicolas Maduro an illegitimate leader. He was elected to a second term last year in a vote widely condemned as sham democracy, as he had barred -- through a justice system stacked with political allies -- all serious opposition candidates.

Venezuela's National Assembly head and self-proclaimed "acting president" Juan Guaido speaks to the press after attending a mass in honour to the fallen in the fight for freedom, political prisoners and the exiled, at the San Jose church in Caracas, Jan. 27, 2019. Getty

Guaidó, while now recognized by many nations as the legitimate leader of Venezuela, remains in hiding as Maduro still has the support of the country's security forces -- and some major international allies including China and Russia. Russia, and America's NATO ally Turkey, have rejected Guaidó's bid to take over as a U.S.-backed coup.

On Monday, the Trump administration upped the pressure on Maduro, slapping new sanctions on the state-run oil company Petróleos de Venezuela, S.A., or PdVSA.

President Trump's National Security Advisor John Bolton the sanctions amounted to, "$7 billion in assets blocked today, over $11 billion in lost export proceeds over the next year." Mnuchin said the U.S. would "continue to use economic, diplomatic tools to support the Venezuelan people's efforts to restore their economy."

The Trump administration said the sanctions were aimed at blocking Maduro from using the country's oil wealth to keep propping up his regime and going after his opponents. The Treasury Department said the sanctions would be lifted if and when Guaidó assumes control of the government.

Guaidó told Britain's Sky News in an interview aired Tuesday that he welcomed the U.S. sanctions and would continue to lead and call for the protests, which are aimed at forcing Maduro to call new elections.

Russia, which has extensive commercial interests in Venezuela, including Russian state oil company Rosneft's partnership with PdVSA, called the new U.S. sanctions "illegal."

Kremlin spokesman Dmitry Peskov said Moscow views the sanctions as a tool of unfair competition on the part of the United States.