* China factory sector slackens in August
* Speculators raise bullish copper positions in latest week
* U.S. markets closed for Labor Day holiday (Updates with closing prices)
By Harpreet Bhal and Eric Onstad
LONDON, Sept 1 (Reuters) - Copper prices fell on Monday, under pressure as weak factory data from China raised concerns about the outlook for demand from the world's top metals consumer.
Three-month copper on the London Metal Exchange closed down 0.6 percent at $6,942 a tonne after ending August down 1.9 percent - its first monthly loss in four months.
Volumes were subdued as markets in the United States were shut for the Labor Day holiday. At the close of open outcry trading, 7,750 lots of copper had traded versus a total volume of 13,765 on Friday. Electronic trading was continuing after the close of ring trading.
Growth in China's vast factory sector slackened in August as foreign and domestic demand slowed, stoking speculation that further policy easing would be needed to prevent the economy from stumbling once more.
China is the world's largest copper consumer, accounting for as much as 40 percent of global demand.
"The Chinese manufacturing data once again increased speculation that the (world's) second-biggest economy is slowing down and this has made traders cash in some of their chips," said Naeem Aslam, chief market analyst at Ava Trade.
Some analysts said copper prices could be hitting a floor, supported by hopes the Chinese government will implement further economic stimulus measures in a move that is likely to help spur demand for copper.
"We are still expecting both seasonal and fundamental improvement in end-user demand. It's mostly a reflection of credit conditions that take a few months to filter through to industrial commodity demand," said analyst Ivan Szpakowski of Citi in Shanghai.
"The real estate market is one that is probably going to take longer to become a positive contributor, so the recovery this time around is probably not going to be as fast as it has been in other cycles."
Investor concern that further supplies were coming to the market were reinforced by news that Newmont Mining Corp planned to resume copper concentrate exports this week, a Indonesian mining ministry official said.
Hedge funds and money managers raised net long position in copper in the week to Aug. 26, data from the Commodity Futures Trading Commission showed, suggesting investors became more hopeful over global economic prospects.
Markets, however, remained cautious about turmoil in Ukraine.
Ukrainian President Petro Poroshenko accused Russia on Monday of "direct and open aggression" which he said had radically changed the battlefield balance as Kiev's forces suffered a further reverse.
In other metals, nickel dipped after touching three-week lows on Friday, ending the day down 0.3 percent at $18,745 a tonne.
"While the nickel rally has stalled ... and the timing of the next move up is difficult to discern, we advise investors to be patient," analyst Barry Ehrlich at Citi said in a note. "Our commodity team's 2015 nickel forecast of $24,125 per tonne remains realistic, we believe."
LME aluminium ended down 0.1 percent at $2,095 a tonne, not far from last week's 18-month peak of $2,119.50. Aluminium was the top performer among LME metals in August, climbing 5.5 percent on tight immediate supply.
Global exchange stocks of aluminium have been stuck in long queues at warehouses, whose operators typically brought in more metal than they delivered out. That has inflated costs and triggered a raft of class actions by irate consumers.
But a U.S. judge on Friday dismissed antitrust litigation accusing Wall Street banks and commodity merchants, including Goldman Sachs Group Inc and Glencore Plc, of conspiring to drive up aluminium prices by reducing supply.
Zinc closed down 0.1 percent at $2,357 a tonne, and lead finished 0.4 percent weaker at $2,233. Tin failed to trade in closing open outcry activity and was last bid down 1.1 percent at $21,625.
Three month LME copper
Most active ShFE copper
Three month LME aluminium
Most active ShFE aluminium
Three month LME zinc
Most active ShFE zinc
Three month LME lead
Most active ShFE lead
Three month LME nickel
Three month LME tin (Additional reporting by Melanie Burton in Sydney; editing by David Evans and Jane Baird)