Luiz Inácio Lula da Silva’s presidential campaign has accused Donald Trump of wanting to “colonise” Brazil in order to capture its natural resources by meddling in next month’s presidential election.

The accusation came in a televised campaign advert that was broadcast on Thursday by Lula’s team amid growing fears over the impact alleged US interference could have on the vote.

The TV spot claimed the US president was trying to sway the election in favour of Lula’s far-right adversary in the election, Flávio Bolsonaro, in order to advance Trump’s interests in the South American nation.

“Flávio Bolsonaro is Trump’s candidate and what Trump wants is to colonise Brazil, take our riches, steal our future and leave us in the dust,” the female narrator tells viewers in the minute-long video.

The state department has denied claims the US is meddling in Brazil’s election. “Any insinuation of a ‘ploy’ to undermine a democratic nation’s election is a baseless lie,” it said last month in a statement.

Writing on X, Lula accused Bolsonaro of wanting to “hand our natural resources over to the United States”.

“If it’s up to him, Brazil will become a colony again,” the incumbent leftwing president added.

With just over a week to go until the 4 October first round vote, Lula and Bolsonaro are neck and neck in the polls. A second round run-off will be held on 25 October if no candidate secures more than half of the votes.

In recent weeks, there has been growing alarm – both in Brazil and overseas – about Washington’s apparent attempts to influence the result, with a campaign of diplomatic and economic pressure, including 25% tariffs on Brazilian imports.

Speaking at the UN general assembly in New York this week, Lula indirectly criticised the US’ perceived meddling, telling delegates: “We will not allow the enemies of democracy – internal or external – to attack the will of the people. Brazilian democracy belongs to the Brazilians.”

Earlier this week, dozens of Democratic party congresspeople wrote to secretary of state, Marco Rubio, to denounce the Trump administration’s “apparent effort to interfere with, and potentially undermine” Brazil’s elections through what they called a “sustained, multifaceted campaign of interference and destabilisation in Brazil”.

The narrator of Lula’s campaign ad cited a series of recent media stories relating to alleged acts of US meddling.

They include reports about the alleged interference of Big Tech companies as well as a confidential document sent to electoral authorities by Brazil’s intelligence agency warning of a “critical level” of risk of US interference. The campaign video also highlighted recent claims about links between Bolsonaro’s campaign and the conservative donor network Rockbridge, which was co-founded by Trump’s vice-president JD Vance.

Éden Valadares, the communications secretary for Lula’s Worker’s party (PT), said the campaign ad was part of efforts to “alert the Brazilian people” to the ideologically-driven US campaign. “We don’t believe it will work but nor will we sit back and do nothing,” Valadares said.

“President Lula has instructed us … to mobilise Brazilian society … [and] to react in the streets,” added Valadares, who said a nationwide series of events were being planned for this Sunday.

Fears over US meddling are not confined to the Brazilian left. This week, another of the right-wing candidates in Brazil’s election, Renan Santos, also denounced Trump’s behaviour and said he did not want Brazil to become a US vassal state. “They want to interfere in Brazil’s elections to secure satisfactory contracts involving rare earths,” Santos claimed in a social media video.

Recalling the US invasion of Venezuela in January, Santos added: “I don’t want to see Latin America become an American protectorate.”

In the letter sent to Rubio on Friday, the Democratic lawmakers wrote that “rather than helping defend Brazilian democracy”, the US was “acting as an agent of interference and destabilisation – using diplomatic, economic and political pressure in ways that risk weakening the country’s democratic institutions, undermining confidence in Brazil’s electoral process, and inflicting further damage on our relationship with a strategic US ally and trading partner”.

They asked Rubio if Trump’s administration would commit to respecting Brazil’s electoral process and requested a response by 1 October. The state department has not yet responded to a request for comment.