The service will remain available to Brazilian users.
The closure was the apparent culmination of an ongoing legal battle between Musk and Brazilian Supreme Court Judge Alexandre de Moraes, who has said he is trying to fight the spread of dangerous disinformation online.
A post Saturday from X's Global Government Affairs department said Moraes had "threatened our legal representative in Brazil with arrest if we do not comply with his censorship orders."
It said the office closure was necessary "to protect the safety of our staff," adding, "the responsibility lies solely with Alexandre de Moraes."
The Brazilian government was critical of X's stance, with Secretary of Digital Policies Joao Brant writing on the platform that the company had a "pathetic attitude."
He added that X would force a "probable escalation that could lead to blocking of the platform."
Moraes previously had ordered the suspension of several Twitter accounts suspected of spreading disinformation, including those of supporters of former far-right president Jair Bolsonaro, who tried to discredit the voting system in the 2022 presidential election, which he lost.
"Freedom of expression doesn't mean freedom of aggression," Moraes has said. "It doesn't mean the freedom to defend tyranny."
Moraes has spearheaded the battle against disinformation in South America's largest nation.
He presides over Brazil's Superior Electoral Tribunal (TSE), and last year it declared Bolsonaro ineligible to run again for office, saying he had disseminated false information about the electoral system.
Musk and other critics have said Moraes is part of a sweeping crackdown on free speech.
The CEO said Saturday that had X complied with Moraes's orders, "there was no way we could explain our actions without being ashamed."
In April, Moraes ordered an investigation of Musk. An order seen by AFP showed Moraes accusing Musk of "criminal instrumentalization" of the platform.
Moraes said Musk had reactivated banned accounts, and he threatened the billionaire with a fine of about $20,000 for each instance.
"Social networks are not lands without laws," Moraes wrote.
Musk responded that while X might lose its Brazilian revenue, "principles matter more than profit."
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