The deputy president is one of the two leading candidates vying to take over from President Uhuru Kenyatta after the vote. His main rival is former prime minister Raila Odinga.

Mr Ruto told European Union ambassadors during a meeting that a million voters had allegedly been moved off the voting roll from his strongholds by the Independent Electoral and Boundaries Commission (IEBC).

But IEBC chairman Wafula Chebukati said there was no "breach of the voter register or interference of the system that holds it".

“Let's not talk about one million names missing, there's no such thing. The one million names we are talking about are for those who applied for transfers and we are undergoing the process of ensuring that the proper transfers are affected," he said.

On Thursday, the deputy president accused government officials of taking sides in the forthcoming poll.

Mr Ruto has also pulled out of a presidential debate scheduled for July, citing biased media coverage.