UPDATE 1-ETF Securities Physical Gold ETC holdings down 16 pct

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LONDON, Sept 15 (Reuters) - ETF Securities said on Monday the amount of metal it held to back its Physical Gold exchange traded commodity (PHAU.L) fell 16 percent in the week to Sept. 14.

The ETC now holds 1.551 million ounces of gold, down 300,000 ounces week-on-week to its lowest level since mid-July. Spot gold XAU= prices have slipped some 20 percent in the same period.

The company's Physical Silver (PHAG.L) ETC saw its holdings tick up by 3 percent in the same period, however, to 11.41 million ounces, their highest level since early February.

Analysts say silver's larger price drop of recent months, in comparison to gold, may be encouraging investment at lower prices.

The company's Physical Platinum and Palladium ETC holdings were unchanged from a week ago.

(Reporting by Jan Harvey; editing by Christopher Johnson)