A fire which has been alight on Saddleworth Moor for more than a week is now being investigated as arson, Greater Manchester Police has said.
Crews are into the second week of fighting the blaze in Tameside, east of Manchester.
Now Greater Manchester Police has said the fire is being investigated as a deliberate attack.
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In a statement issued through Greater Manchester Police, Interim Chief Fire Officer Dawn Docx said: "Specialist fire investigation officers at Greater Manchester Fire and Rescue Service are working closely with Greater Manchester Police to investigate the suspected arson in the moorlands in Tameside.
"Investigations are currently ongoing with a multi-agency approach to find the source of the ignition. There is an area of interest that specialist officers are inspecting.
"Firefighters are working in extremely difficult and challenging circumstances in Tameside and I can't praise crews enough - they've done a fantastic job and are continuing to work hard to put out the multiple fires across the moorlands.
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"I would like to urge the public to be really careful with barbecues, discarded cigarettes and glass bottles in the countryside, fires in the moorlands can spread rapidly so it's important that we take extra care."
Yesterday, some 45 firefighters remained at the scene above Stalybridge with support from crews from the West Midlands, South Yorkshire, Gloucestershire and West Yorkshire, plus the ongoing assistance of troops from the Royal Regiment of Scotland (4 SCOTS).
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Crews have been using specialist vehicles including four high volume pumps and a helicopter to dampen down the blaze from height and fight the fire.
Meanwhile 35 GMFRS firefighters have been supporting 140 colleagues from Lancashire in their battle to maintain control of a blaze at Winter Hill which broke out when two moorland fires either side of the hill merged on Saturday because of increased wind speed.