LONDON: Copper prices slipped on Thursday as investors questioned whether its recent rally was exaggerated and were cautious ahead of a meeting of the European Central Bank (ECB).

Copper, which has rebounded about 50% from 45-month lows in March, is the best-performing industrial metal this year, helped by a recovery in top metals consumer China and tumbling inventories.

Three-month copper on the London Metal Exchange was down 1.1% at $6,655 a tonne at 1015 GMT, after rising on Wednesday.

LME copper inventories ticked higher on Thursday after repeatedly touching the lowest levels since 2005 in recent weeks.

"That raised the question of whether for copper we have priced in most of the supportive news in terms of declining stocks and Chinese data. That leaves the market somewhat focused on what happens on the macro front," said Ole Hansen, head of commodity strategy at Saxo Bank in Copenhagen.

"Having failed above $6,800, the really big number for copper is the uptrend from the March low and that's coming in at $6,550, which if broken could add additional selling pressure."

The euro edged higher, but gains were capped by the possibility the ECB could flag more policy easing.

A stronger euro makes metals priced in dollars cheaper for buyers using the euro.

Benchmark treatment charges for copper concentrate next year are likely to fall for a sixth straight year to their lowest since 2011 at about $60 a tonne.

LME lead inventories rose to 131,750 tonnes, the highest since June 2018, having more than doubled over the past two months.

The discount of LME lead cash to the three-month contract rose to $28.75 a tonne, the highest since November 2018, indicating healthy supplies.

LME aluminium edged down 0.4% to $1,777 a tonne, nickel fell 0.9% to $14,790 and tin shed 0.3% to $17,960.

Lead dropped 1.2% to a one-month low of $1,871.50 while zinc lost 1% to $2,400 after touching $2,385, the weakest in over three weeks.