The party’s candidate, Warsaw mayor Rafal Trzaskowski, is polling first in opinion surveys before round one of the ballot on Sunday.

“Since 9am there has been an ongoing DDoS (distributed denial of service) attack against the Civic Platform (PO) site,” said Jan Grabiec, the prime minister’s chief of staff.

“PO’s main page and an additional one devoted to campaign donations have been temporarily disabled,” he added on X, without identifying the source of the cyberattack.

Grabiec said the party was working on getting the website back up and running.

NASK, a national research institute specialising in cybersecurity, had reported yesterday attempts to interfere in the election campaign via messages consistent with Russian propaganda.

Last month, the ministry of digital affairs said Russian cyberattacks against Poland had intensified.

Also in April, prime minister Donald Tusk said his party’s computer system had been the target of a cyberattack, which he described as “foreign interference”.

Thirteen candidates of all stripes are vying to be the next president of the EU and Nato country of 38 million people.

Trzaskowski is currently the frontrunner, with around 30% of the vote in the latest opinion polls.

Nationalist historian Karol Nawrocki, endorsed by the right-wing main opposition Law and Justice (PiS) party, is polling in second place at around 25%.

Analysts have said the future of Poland’s pro-EU government is riding on the presidential elections, which come at a fraught moment for Europe.