* London stock market closed on Monday
* FTSE 100 down 0.1 pct, falls off 3-week highs
LONDON, Aug 22 (Reuters) - Britain's top equity index slipped off three-week highs on Friday, with mining stocks among the worst performers as weak metals prices weighed on the sector.
The blue-chip FTSE 100 index was down by 0.1 percent, or 8.29 points, at 6,769.37 points going into the close of trading. The London stock market is closed for a public holiday on Monday.
Gold and silver miner Fresnillo was the worst-performing FTSE 100 stock in percentage terms, falling 2 percent as the price of gold remained stuck near a two-month low.
Traders pointed to a dovish tone in a speech on Friday by U.S. Federal Reserve Chair Janet Yellen as limiting the stock market's losses.
Yellen said the Fed should move cautiously in determining when interest rates should rise.
Nevertheless, equity traders remained on the backfoot, with tensions in Ukraine - where Kiev said Moscow sent a convoy of aid trucks into eastern Ukraine without its consent - also weighing on stock markets.
The FTSE 100 hit a peak of 6,894.88 points in mid-May, its highest level since December 1999, but the market has since given up much of that ground due partly to worries over conflicts in Ukraine and also in Iraq.
Basil Petrides, sales trader at Beaufort Securities, said investors could be tempted to sell out and book profits if the FTSE could not break above previous highs in the 6,830-6,890 points range set in the last two months.
"If it does not take out those previous highs, then it could lead to a minor pullback," he said.
Others were a bit more positive on the FTSE's prospects, with the UK stock market buoyed by Britain's gradual economic recovery and a pick-up in corporate takeover activity.
Carlo Alberto de Casa, senior market analyst at online brokerage ActivTrades, said the FTSE could climb to 6,825-6,830 points if it broke above the 6,785 point level.
"The longer-term trend still looks positive," he said. (Additional reporting by Atul Prakash; Editing by Mark Heinrich and Susan Fenton)