Venezuela has said that its border with Colombia has been partially closed, shortly after opposition leader Juan Guaidó defied a travel ban to cross it.
Vice President Delcy Rodriguez tweeted to say the “total, temporary closure” was due to serious threats against the country’s sovereignty and security.
Tensions have been rising over a row about the delivery of humanitarian aid.
Two people were killed by Venezuelan security forces on Saturday near the border with Brazil.
The violence has been condemned by the White House, which reiterated in a statement that “the world is watching”.
Mr Guaidó, the leader of the country’s opposition-dominated National Assembly, declared himself the country’s interim leader last month.
He has since won the backing of dozens of nations, including the United States.
He argues Mr Nicolas Maduro’s rule is constitutionally illegitimate because his re-election in 2018 was flawed, and has vowed to oversee fresh elections.