The Brazilian government has blocked a U.S. delegation from traveling to the country next week, concerned that the visitors would seek to cast unfounded doubts on the safety of the nation’s electoral systems ahead of a presidential contest this year, according to U.S. and Brazilian officials.

The U.S. delegation included two senior State Department officials, Riley M. Barnes and Samuel Samson, according to three senior U.S. and Brazilian government officials, who spoke anonymously to discuss confidential diplomatic matters. On Friday, Brazilian authorities rejected their requests for a visa, according to two of those officials, derailing the planned visit.

A spokesman for Brazil’s foreign ministry confirmed the visa rejections but did not provide a reason.

The State Department confirmed that Mr. Barnes and Mr. Samson were set to travel to Brazil next week to hold meetings about election integrity, religious freedom and freedom of expression. “Any insinuation of a ‘ploy’ to undermine a democratic nation’s election is a baseless lie,” the department said in a statement.

In the visa application, submitted on Monday, the U.S. officials said they planned to meet with electoral authorities to discuss Brazil’s voting systems and concerns about possible restrictions to the freedom of expression in the lead-up to the Oct. 4 elections, according to one of the Brazilian officials.

The decision to bar the U.S. delegation is the latest escalation between the nations after several weeks of heightened tensions following new tariffs and ideological clashes on issues like organized crime.

It also fuels concerns among many Brazilians over possibly more meddling by President Trump in Brazil’s internal affairs, this time aiming for a voting system that global observers widely regard as secure. At the same time, the move to bar the delegation risks stoking complaints from conservatives in both countries about a lack of transparency ahead of the high-stakes election.

In a region where the right is fast ascending, Brazil’s electoral contest, which will pit a leftist incumbent against a right-wing challenger, will serve as the left’s biggest test this year.

Mr. Barnes and Mr. Samson also planned to meet with Flávio Bolsonaro, the son of former President Jair Bolsonaro, who is serving a 27-year sentence for plotting a coup, according to the officials. The younger Mr. Bolsonaro is challenging the leftist incumbent, Luiz Inácio Lula da Silva, for the presidency. He has made multiple trips to Washington in recent months, some of them to seek support for his political agenda.

At an event with diplomats this week, Mr. Bolsonaro took a page from his father’s playbook and questioned the security of Brazil’s electronic voting machines using debunked claims about their susceptibility to fraud. Ahead of the previous election, the elder Mr. Bolsonaro made similar claims in front of a group of diplomats.

Experts widely regard the South American nation’s voting systems, which use biometrics to identify voters and tallies results almost immediately after polls close, as some of the most secure in the world. The country’s elections are regularly monitored by dozens of observers from around the world.

“To date, we have had no evidence of fraud in the voting process,” said Estela Aranha, a justice on Brazil’s electoral court, which oversees the federal vote. She added that the process is verifiable and transparent.

Mr. Bolsonaro’s complaints about electoral security come as his campaign falters, following revelations about his ties to a disgraced banker. Early polls showed Mr. Bolsonaro and Mr. Lula locked in a close race, but a new poll this week showed the leftist incumbent’s lead has widened significantly.

And after Mr. Bolsonaro’s statements this week, Brazilian authorities became convinced that the U.S. delegation was not on a fact-finding mission, but rather planned to undermine confidence in the country’s voting systems, said the two Brazilian officials.

Mr. Barnes, an assistant secretary, and Mr. Samson, a deputy assistant secretary, do not have expertise or significant experience in Brazil, according to one U.S. official. Mr. Samson has played a key role in pushing Mr. Trump’s agenda in Europe, cultivating ties with right-wing groups aligned with his movement.

Brazil’s electoral court said in a statement that U.S. diplomats in the country had inquired about a possible visit by American officials, without disclosing the agenda. The meeting was ultimately not scheduled because the court is in recess.

In June, the court’s lead justice, Kássio Nunes Marques, addressed some two dozen ambassadors to explain the workings of the Brazilian voting system. U.S. diplomats were invited but did not attend, according to the event organizers. The court said it plans to hold another meeting next month and will invite U.S. representatives.

Earlier this year, the Brazilian government barred another Trump envoy from entering the country, after learning that he secretly planned to visit the jailed former president and meet his son, Flávio Bolsonaro.

Last year, Mr. Trump tried to pressure Brazil to drop the case against the elder Mr. Bolsonaro, a close political ally, by using hefty tariffs and sanctions.

That strategy didn’t work, and Mr. Bolsonaro was sentenced to nearly three decades in prison for trying to cling to power after losing the 2022 election to Mr. Lula. Mr. Bolsonaro is serving his sentence under house arrest for health reasons.

Thayz Guimarães contributed reporting from Brasília, and Leonardo Coelho contributed research from Rio de Janeiro.