Britain's FTSE set to snap three-week streak of gains

(ADVISORY- Reuters plans to replace intra-day European and UK stock market reports with a Live Markets blog on Eikon - see cpurl://apps.cp./cms/?pageId=livemarkets for site in development. See the bottom of the report for more details)

* FTSE 100 down 0.7 pct

* Commodities companies under pressure

* Burberry down on Kering (LSE: 0IIH.L - news) readacross

* Sainsbury (Amsterdam: SJ6.AS - news) rises on upgrade

By Kit Rees

LONDON, April 22 (Reuters) - UK shares extended their losses from the previous session on Friday when resources companies fell and shares in Burberry dropped as the European luxury sector came under pressure.

The blue chip FTSE 100 index was 0.7 percent lower at 6,338.86 points by 0826 GMT, set to snap a three-week streak of gains.

The FTSE 100 has slipped this week from its highest close since early December, closing at 6,410.26 points on Wednesday.

Mining companies led the index lower, with Rio Tinto (LSE: RIO.L - news) , Anglo American (LSE: AAL.L - news) , Antofagasta (Other OTC: ANFGF - news) and Glencore (Xetra: A1JAGV - news) all down between 1.4 to 2.3 percent as copper prices retreated.

"Commodities have had a spectacular run over the last few months, but that doesn't really change the fundamental story," Chris Beauchamp, analyst at IG (LSE: IGG.L - news) , said, adding that any more upside in the miners looked limited at the moment.

Oil & gas companies BP and Royal Dutch Shell (Xetra: A0ET6Q - news) also declined, both down 1.3 percent and collectively taking around 8 points off the index.

"We've seen a bit of momentum fading in terms of the rally, and I think if you get WTI (crude) moving lower at the beginning of next week, you might see a continuation of this," said IG's Beauchamp, adding that there was some nervousness ahead of BP's figures next Tuesday.

Luxury goods group Burberry was 1.4 percent lower after French peer Kering posted a slowdown in growth at its flagship Gucci brand.

Among the risers, however, British grocer Sainsbury was up 1.7 percent on the back of an upgrade from investment bank Deutsche Bank (LSE: 0H7D.L - news) , which raised its rating on the stock to "buy" from "hold".

Likewise supermarket peers Tesco (Xetra: 852647 - news) and Morrison advanced 1.7 percent and 0.7 percent respectively.

Equipment rental company Ashtead was up 2.2 percent, building on gains from the previous session after posting an upbeat set of full year results.

ADVISORY- Reuters plans to replace intra-day European and UK stock market reports with a Live Markets blog on Eikon (see cpurl://apps.cp./cms/?pageId=livemarkets for site in development). In a real-time, multimedia format from 0600 London time through the 1630 closing bell, it will include the best of our market reporting, Stocks Buzz service, Eikon graphics, Reuters pictures, eye-catching research and market zeitgeist. Breaking news and dramatic market moves will continue to be alerted to all clients and we will continue to provide a short opening story and comprehensive closing reports.

If you have any thoughts, suggestions or feedback on this, please email mike.dolan@thomsonreuters.com.

Mike Dolan, Markets Editor EMEA. (Reporting by Kit Rees)