NEW YORK (Reuters) - Motorola Inc (MOT.N: Quote, Profile, Research) shares slumped 7 percent on Monday to their lowest levels in five years after analysts downgraded the mobile-phone maker on fears it cannot staunch market share losses in North America.

Piper Jaffray analyst T. Michael Walkley cut his rating on Motorola shares to "sell" from "neutral," and his price target to $7 from $9.75 on concerns about falling market share.

"Our checks indicated declining Motorola sell-through trends at all four major North American carriers," he wrote.

The North America market represents nearly half of global unit sales for Motorola. The No. 3 U.S. mobile provider has already been under pressure for its failure to come up with a strong handset line-up since launching the Razr in late 2004.

Avian Securities analyst Matt Thornton also said on Monday that his research had led him to cut his rating on Motorola to "neutral" from "positive."

The downgrades, which followed a similar move by broker RBC last week, dragged the shares down 56 cents to $7.38 by mid-afternoon trading.

That extended a five-day losing streak, which has led to a decline of 19 percent from a week earlier. Motorola shares have lost nearly 60 percent of their value over the past year.

Monday's sell off also follows a flurry of product announcements by rivals.

In addition to Apple Inc's (AAPL.O: Quote, Profile, Research) new iPhone, Motorola faces competition from Sprint Nextel Corp (S.N: Quote, Profile, Research) which last Wednesday priced Samsung Electronic's (005930.KS: Quote, Profile, Research) touch-screen Instinct phone at a competitive $130 after rebate. Sprint said it would spend more than $100 million to market the product.