HELSINKI, FINLAND: Nokia, the world's top cellphone maker, said Stephen Elop, the head of Microsoft's Business Division, was to be its new chief executive.

Elop will take over from Olli-Pekka Kallasvuo on September 21, Nokia said on Friday.

"His (Elop's) strong software background and proven record in change management will be valuable assets as we press harder to complete the transformation of the company," Nokia chairman Jorma Ollila said.

Under Kallasvuo, Nokia has struggled to keep up with new rivals like Apple and Google in the smartphone market, which affected its profits too.