The Democratic National Committee has contacted the FBI, but officials say it was not known who was behind the attack

The Democratic National Committee (DNC) has contacted the FBI after detecting a possible attempt to hack its voter database, which contains information for tens of millions of voters across America.

The disclosure comes just months before the 2018 midterm elections and marks the latest indication that external powers might still be engaged in active efforts to infiltrate the US electoral process. The news was first reported by CNN and was confirmed by the Guardian.

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It was not immediately known who was behind the latest attempt to penetrate the DNC system, officials said, while noting the effort was thwarted.

“This attempt is further proof that there are constant threats as we head into midterm elections and we must remain vigilant in order to prevent future attacks,” the DNC’s chief security officer, Bob Lord, said in a statement.

“While it’s clear that the actors were going after the party’s most sensitive information – the voter file – the DNC was able to prevent a hack by working with the cyber ecosystem to identify it and take steps to stop it.”

The DNC was at the center of Russian interference in the 2016 presidential election, when hackers illegally obtained and subsequently leaked thousands of internal emails through WikiLeaks just ahead of the party’s national convention. Russian hackers subsequently stole more than 50,000 emails from John Podesta, then the chairman of Hillary Clinton’s campaign, and released them in tranches in the months before the November election.

Robert Mueller, the special counsel overseeing the FBI’s investigation into Russian meddling in the US election, indicted 12 Russians last month in connection with the DNC and Podesta hacks. The DNC separately filed a lawsuit earlier this year seeking millions in damages from the Russian government, the Trump campaign and WikiLeaks, claiming a widespread conspiracy to influence the 2016 election.

US intelligence officials have repeatedly warned of “pervasive” efforts by Moscow to disrupt the 2018 midterms, even as Donald Trump has shown little regard over the matter. The president ignited a firestorm last month at a summit with the Russian president, Vladimir Putin, in Helsinki, in which Trump sided with the Kremlin over US intelligence authorities on whether Moscow had interfered in the 2016 election. Although Trump later walked back his comments, amid an avalanche of criticism, he has continued to downplay the threat posed by the Russians in a high-profile split from the national security community.

On Tuesday, Microsoft accused the Russian group linked to the hacking of Democrats in 2016 of launching fresh attacks against political groups in the US. The technology company said it had uncovered fake websites designed to mimic two conservative thinktanks and other fake domains purporting to belong to the US Senate.