Hackers have stolen 2.3 million dollars (£1.93m) from the Wisconsin Republican Party’s account that was being used to help re-elect Donald Trump in the battleground state, the party’s chairman has said.

The party noticed the suspicious activity on October 22 and contacted the FBI a day later, Republican Party chairman Andrew Hitt said.

Mr Hitt said the FBI is investigating.

“There’s no doubt RPW is now at a disadvantage with that money being gone,” Mr Hitt said. The party and campaign needs money late in the race to make quick decisions, he said.

Mr Hitt said the hackers were able to manipulate invoices from four vendors who were being paid to send out direct mail for Mr Trump’s re-election efforts and to provide pro-Trump material such as hats that could be handed out to supporters.

Invoices were altered so when the party paid them, the money went to the hackers instead of the vendors, Mr Hitt said.

He said it appears the attack began as a phishing attempt.

Mr Trump won Wisconsin by fewer than 23,000 votes in 2016 and it remains a key swing state this year.

He is planning his third visit to the state in a week on Friday. Democrat Joe Biden also plans to campaign in Wisconsin on Friday.