HELSINKI, November 18, 2010 (AFP) - Fitch ratings agency said Thursday it was downgrading Finland's Nokia, the world's top mobile phone maker, because the company faced a series of challenges on several fronts.

The Nokia rating was reduced by one notch to BBB+ from A-, with the outlook negative, meaning that the company is likely to face further problems.

"The company's core handsets position is facing increased competition in both the high-end 'smartphone' segment in mature Western markets as well as lower-end emerging markets like China and India; markets which have traditionally been strengths for Nokia," Fitch said.

"In such a fast changing industry a misstep in technology can lead to material loss of market share, with Fitch estimating that Nokia's overall handset share fell to 28 percent in third quarter 2010 from 37 percent in third quarter 2009," it said.

Fitch noted that Nokia's Symbian operating system was also losing market share, it added.

In October, Moody's lowered its rating outlook on Nokia to "negative" from "stable" on concerns over whether it could reverse the loss in market share.