London: Copper prices fell on Thursday as weak German factory data underlined concerns about the outlook for demand and a big inflow of metal into London Metal Exchange (LME) warehouses suggested supply was adequate.
Other industrial metals also slipped despite positive signals from US-China trade talks.
Benchmark copper on the LME did not trade in official rings but was bid down 0.5% at $6,460 a tonne.
The metal, used in power and construction, has risen from an 18-month low of $5,736 in January on hopes that China, the largest consumer, can prevent a sharp economic downturn.
But prices have remained stuck around current levels since late February.
"$6,500 appears to be a bit of a barrier," said Capital Economics analyst Ross Strachan.
Copper supply is tight, but deteriorating economic growth in Europe, China and the United States will sap demand, he said, predicting prices would fall slightly over the year.
German factories: German industrial orders fell by 4.2%, their sharpest rate in more than two years, in February, hit by a slump in foreign demand.
Trade talks: US-China trade talks made "good headway" last week and the two sides aim to bridge differences during talks that could extend beyond three days this week, White House economic adviser Larry Kudlow said.
Global markets: European and Asian shares slipped from 8-month highs, though Chinese shares rose.
Las Bambas: A Peruvian judge ordered three years of jail time for three lawyers representing indigenous villagers who have blockaded shipments from a massive copper mine, worsening the dispute.
Copper stocks: Copper inventories in LME-registered warehouses leaped by 30,375 tonnes to 198,325 tonnes, the highest in six months and nearly double the level three weeks ago.
Total stockpiles in LME, Comex, Shanghai Futures Exchange and Chinese bonded warehouses have risen by close to 300,000 tonnes this year, according to analysts at Barclays.
Copper spread: Cash copper on the LME has flipped from a hefty premium over the three-month contract to a $13.25 discount, suggesting a shortage of nearby metal has eased.
TIN: LME tin traded down 0.1% at $21,150 a tonne, even with stocks in LME warehouses at a record low of 920 tonnes . The premium for cash tin over three-month metal jumped to $137.50 from $49 on Monday, pointing to a shortage of immediately available metal.
China holiday: The Shanghai Futures Exchange will be closed on Friday for the Tomb Sweeping Day holiday in China.
Other metals: LME aluminium traded down 0.2% at $1,892 a tonne, nickel was bid 1.9% lower at $13,120, zinc was bid down 0.4% at $2,919 and lead traded down 0.4% at $2,006.