|Klitschko retained his two belts by knocking out Eddie Chambers in March [EPA]
Wladimir Klitschko says his desire to fight David Haye is "personal" after the Ukrainian released a YouTube video challenging the British boxer.
And he believes it is time for him and his brother Vitali to unite the world heavyweight titles under one name by Taking Haye's WBA title.
Wladimir, 34, holds the WBO, IBF and IBO belts while Vitali is the WBC champion.
Former cruiserweight champion Haye retained his WBA belt earlier this month with a technical knockout over John Ruiz.
"It is now time to unite all belts under one name – the Klitschko name," Wladimir told the Reuters news agency by telephone from Los Angeles on Tuesday.
"It is up to Haye. I have never been so aggressive in wanting an opponent but this is personal."
The Ukrainian, who has a record 54 wins and three losses, recorded a last-gasp knockout of American Eddie Chambers in March.
"Don't be a coward, David. In the name of all boxing fans I officially challenge you to fight me. You cannot keep running away from me"
Wladimir Klitschko, WBO, IBF and IBO champion
And while the brothers will not fight each other, a possible showdown with Haye this year is a major attraction for broadcasters.
"It is definitely going to be a big deal for television," said the Ukrainian.
"It is going to be an historic event when all the belts will have one name.
"I am the world champion and I will prove it.
"Haye is good and he will challenge me but this time you will not see defensive boxing as in my last few fights. I will be more aggressive."
Haye, 29, who has a 24-1 record, has said the Klitschko brothers consistently pick "over-the-hill" opponents.
They, in turn, have accused the Englishman of twice scuppering their plans to fight him last year.
Haye also angered the pair when he appeared at a news conference wearing a T-shirt that depicted him holding the bloodied and severed heads of the Klitschkos.
"Haye cannot be trusted. We twice wanted to fight him but he always pulled out," said Wladimir.
"He had promised Chelsea Football Club's stadium then he said 'Let's do it in June' (in Germany)...he just cannot be trusted.
"Now it is between me and him. Now I think it is my turn."
In a video message posted on his website on Monday, Germany-based Wladimir said: "Don't be a coward, David...in the name of all boxing fans I officially challenge you to fight me.
"You cannot keep running away from me. I am ready so what are you waiting for?"