KIEL, Germany -- After his latest knockout, Russian heavyweight Wladimir Klitschko is looking for a title fight.

Former WBO champion Wladimir Klitschko stopped overmatched American Danell Nicholson in the fourth round of a non-title heavyweight fight Saturday.

The bout was stopped 1 minute, 16 seconds left in the fourth round as Klitschko battered his opponent on the ropes after knocking him down a few seconds earlier.

The 27-year-old Klitschko is the younger of the two fighting Ukrainian brothers, with brother Vitali also a top heavyweight contender.

"It wasn't easy, but he moved a lot and it isn't easy to hit a moving target," said Klitschko, who improved to 43-2 with 39 knockouts. "But the important thing is it will continue for me and Vitali next year.

After the four-round fight, Klitschko called out any and all of the current champions.

"Now that I have had two tune-up fights, I am definitely ready to fight any of the world champions," Klitschko said. "It does not matter to me which champion I fight."

Klitschko is looking for the same opportunity that his brother, Vitali, had in June against WBC and IBF champion Lennox Lewis.

The champion had some trouble before winning via technical knockout in the sixth round as Vitali Klitschko was not allowed to continue due to a large cut over his eye.

Although Lewis offered a rematch, he also is contemplating retirement, which would leave WBA champion Roy Jones Jr. as Wladimir Klitschko's only option. However, Jones returned to the light heavyweight division for his last fight and may stay there, which would leave John Ruiz as the interim champion.

"Next year is going to be the year of the Klitschko brothers," Wladimir Klitschko said. "I am more than certain that Vitali will win the world title -- hopefully, it will be in the rematch against Lennox Lewis -- and I am confident that I will, too."

Wladimir Klitschko lost his WBO title in March when he was beaten in two rounds by South African Corrie Sanders.

In August, Klitschko knocked out overmatched Fabio Moli of Argentina in 97 seconds.

Nicholson, who record slipped to 42-5 with 32 knockouts, tried to tie up the 6-foot-7 Klitschko from the opening seconds. He was penalized a point for holding in the second and warned again in the third.

"It wasn't working. When it isn't working you try some things," Nicholson said.

The end came quickly as Klitschko knocked him into the ropes with a left hook in the fourth, then followed with some combinations. After Nicholson got back up, the Ukrainian sent him into the ropes again with a short right to the head.

Information from The Associated Press was used in this report.