DAWSON CREEK, B.C. - Police and community leaders fear an anonymous letter warning a "long and hot summer is coming," signals the end of a nine-month lull in bombing attacks against natural gas pipelines in northeastern British Columbia.

The letter, received by a Dawson Creek newspaper Wednesday, was still being authenticated by investigators, but for now police are treating it seriously.

"Our investigators are currently working to try to determine whether the letter is in fact authentic or a hoax," RCMP spokesman Sgt. Rob Vermeulen told The Canadian Press on Thursday.

The letter strikes a similar tone to previous ones, condemning oil and gas development in the region and warning of consequences if energy companies don't pull out.

"This land belongs to us and our children not to you. You are the criminals not us," says the letter, this time typed instead of hand-written.

"Be prepared for action as we intend to fight back with a range (sic) you haven't seen before. Get out of our home lands and stop poisoning us or face the consequences."

There have been six bombings targeting the operations of Calgary-based Encana Corp. (TSX:ECA) since October 2008. The last two explosions were in July 2009.

A letter sent last fall declared a three-month time-out from the bombing campaign but Wednesday's letter said the "time-out is over."

Mayor Lyman Clark of the village of Pouce Coupe, near where some of the attacks took place, said the letter has to be taken seriously for now.

"No chances can be taken with this character," said Clark. "He's already shown his hand, that he's capable of blowing things up."

Vermeulen said the RCMP are taking additional measures to increase public safety.

"There's no specific threat made and there's no specific timeline but obviously our primary concern is for the safety of the residents there," he said.

"Obviously when you have a letter that in this case threatens some sort of action -- whether it's a hoax or not -- you'd better take it seriously from the outset."

Clark said he saw three military helicopters sweeping the area above previous bomb sites Thursday morning, but the RCMP would not discuss what steps they've taken.

In nearby Dawson Creek, the hub of northeast B.C. oilpatch activity, Mayor Mike Bernier said after months of relative quiet, the new letter will ramp up tension.

"I think what'll happen is it'll just remind people that somebody out there is a little unstable," he said.

The letter is the fourth of its kind, including one police determined was a hoax.

The first preceded bombings that targeted Encana operations around the community of Tomslake. The blasts damaged a pipeline carrying so-called sour gas, which contains highly poisonous hydrogen sulphide.

The RCMP have labelled the bombings domestic terrorism and set up a task force led by the Integrated National Security Enforcement Team.

Investigators blanketed the region last year, causing a backlash among some residents who claim they were being intimidated by police.

Encana has offered a $1-million reward for information in the case.

Alan Boras, vice-president of media relations, said the company would not comment on the latest letter since it is part of the police investigation.

But facilities in the region are protected, he said.

"We are comfortable with the security we have in place, and we have ongoing security and we've reviewed that and adjust those plans from time to time," Boras said.

The task force arrested convicted oil well bomber Wiebo Ludwig in January and searched his Alberta farm, but Ludwig was released without any charges 24 hours later. He has said he is not behind the bombings, and doesn't know who is.

Ludwig said Thursday police are taking the wrong approach, especially in their treatment of local residents.

"Instead of listening to the complaints these people have, which are very legitimate ... you bug them and scare the dickens out of them," he said.

Encana is the major player in the oil and gas sector in northeastern British Columbia, where there are more than 4,000 producing wells.

The industry has seen massive growth in B.C. since the mid-90s, with provincial revenues jumping from $370 million in 1996 to $2.5 billion in 2006 -- mostly related to natural gas projects.

Pouce Coupe's mayor said local residents aren't overly frightened by the situation.

"It's a pretty stalwart old bunch of farmers and people of the North," Clark said. "Nobody's happy about it and everybody's hoping nobody gets hurt or anything like that. There's no panic going on or anything like that."