(Adds detail, updates prices) By Melanie Burton MELBOURNE, May 1 (Reuters) - London copper hit its lowest in three weeks on Tuesday, dampened by a stronger dollar ahead of a U.S. monetary policy meeting and by a holiday in top metals user China. Aluminium and zinc prices also came under pressure after the United States delayed aluminium and steel tariffs for some countries and announced permanent exemptions for others, raising the prospect of better metal supply. FUNDAMENTALS * COPPER: London Metal Exchange copper fell to its weakest in three weeks at $6,752 a tonne, accelerating downwards after it broke below the 200-day moving average at $6,800, with the world's top metals buyers absent from the market. * SHFE: The Shanghai Futures Exchange remained closed for a second day of public holidays, reopening on Wednesday. * COPPER DEMAND: Signals from the physical market were mixed. Pointing to healthy demand, ShFE copper stocks fell by 18 percent, or more than 50,000 tonnes, over April, while LME copper set for delivery to consumers jumped by a similar volume.* But in China's domestic market, physical metal has traded at a 250 yuan ($39.48) to 400 yuan discount to the ShFE front-month contract for the past week, the widest in around six months, suggesting tepid demand for spot metal. * TARIFFS: U.S. President Donald Trump has postponed the imposition of steel and aluminium tariffs on Canada, the European Union and Mexico until June 1, and has reached agreements for permanent exemptions for Argentina, Australia and Brazil, the White House said on Monday. * ALUMINIUM: London aluminium had slipped 0.6 percent to $2,242 a tonne by 0727 GMT, while LME zinc, used to galvanise steel, fell 0.8 percent to $3,103.50 a tonne. LME nickel, used by stainless steel makers, climbed 0.2 percent. * RUSAL: U.S. Treasury Secretary Steven Mnuchin on Monday said the United States was not seeking to put Russian metals giant Rusal out of business by hitting it with sanctions, according to an interview with Bloomberg News. * For the top stories in metals and other news, click or DATA/EVENT AHEAD (GMT) 1400 U.S. ISM manufacturing PMI Apr 1400 U.S. Construction spending Mar U.S. Federal Reserve starts two-day monetary policy meeting DATA BASE METALS PRICES 0728 GMT Three month LME copper 6757.5 Most active ShFE copper 0 Three month LME aluminium 2242 Most active ShFE aluminium 0 Three month LME zinc 3103.5 Most active ShFE zinc 0 Three month LME lead 2318 Most active ShFE lead 0 Three month LME nickel 13660 Most active ShFE nickel 0 Three month LME tin 21250 Most active ShFE tin 0 ($1 = 6.3325 Chinese yuan renminbi) (Reporting by Melanie Burton Editing by Joseph Radford)
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