Nokia has begun looking for candidates to replace Chief Executive Olli-Pekka Kallasvuo, who has struggled to keep up with nimbler rivals Apple Inc and Google Inc , the Wall Street Journal reported on Monday.

Kallasvuo may be ousted as early as the end of July, the newspaper cited a person familiar with the matter as saying. A U.S. based spokeswoman for the Finnish cellphone maker declined to comment, citing company policy regarding market rumors.

They are serious about making a change, the source was quoted as saying by the newspaper.

The CEO of one major U.S. high-tech company had spurned Nokia's approach after meeting with Chairman Jorma Ollila, because that candidate had not been keen on moving to Finland, the Journal cited the source as saying.

Nokia had also flown in at least one other U.S.-based executive to interview for the job, the source added.

Kallasvuo has come under attack from shareholders this year as the stock price waned. Nokia warned on Wednesday second-quarter sales and profits at its key phones unit would come in weaker than expected -- the company's second profit warning in less than two months.

Analysts say it has been slow to innovate amid an explosion of feature-rich multimedia gadgets like the Apple iPhone and devices based on Google's Android operating system.

Shares in Nokia fell to their lowest in over a year last week. Analysts say Nokia's market-share position could weaken further in coming months.

(Reporting by Phil Wahba)