Residents are concerned after numerous wildfires on Caerphilly and Rudry mountains in recent months.
Many of the fires have been spotted on Gwern-y-Domen common in particular.
Guy Milnes, who lives in Caerphilly, said: “The fire service and police are in attendance almost every night but it seems there is little they will or can do except contain the fire once it starts. Local residents have spotted a group of around five young teenagers acting suspiciously in the area.
“It is a haven for wildlife including rabbits, birds, insects and rare bees. It is also beautiful walking country providing a wonderful backdrop to dog walkers, families and anyone who wants to escape into the countryside.
“These individuals must be stopped before much more damage occurs and ruins the landscape forever. The situation is becoming ever more urgent as we move into summer and the ground becomes drier.”
Mr Milnes added: “We do not want to have the same headlines as Saddleworth Moor, near Manchester, did during last summer’s wildfire season.”
In July last year, firefighters attended 291 grass fires across Caerphilly County Borough.
A spokesperson for South Wales Fire and Rescue Service said: “We have attended a significant number of deliberate grass fire incidents across South Wales over the weekend, some requiring the attendance of multiple appliances and the movement of resources.
“Deliberate grass fires put lives in danger and cause damage to property and the environment.
“Diverting our resources to deal with grass fires means it can often take longer for us to respond to other emergencies.
“We would urge anyone who has information on grass fires, or who sees anything suspicious to contact 101, or call Crimestoppers anonymously on 0800555111.
“If you see a grass fire, or anyone starting a grass fire, please call 999 immediately.”
Gwent Police Chief Inspector Jason White said: “Local Policing teams within the Caerphilly Borough continue to work alongside their colleagues within South Wales Fire and Rescue to address grass fires. Joint patrols are undertaken in areas deemed to be susceptible to grass fires to provide both reassurance to communities but also a visible deterrent to those intent on causing damage to area.
“Officers seek to engage with individuals located in these areas where advice and guidance are provided in addition to other intervention methods.”
He added: “Gwent Police have an excellent relationship with South Wales Fire and Rescue Service which has been further strengthened with Sergeant Andy Elias currently seconded to the South Wales Fire Crime Unit.
“Andy’s role is pivotal to the success of tackling grass fires in the Gwent area through education and engagement with young people, the sharing of valuable information with partners and co-ordinating proactive joint patrols in vulnerable areas.”