At a Vancouver news conference, the RCMP and officials with EnCana Corp. also called for an end to the attacks, the Vancouver Sun reported.

Three bombs exploded along the line in northeastern British Columbia in October, and the fourth happened last week. No one has been injured by the blasts, and only one small gas leak was caused.

The RCMP said there are residents in the area who have been uncooperative in speaking about the explosions, although there are no suspects, the newspaper reported.

Before the bombings began, an area newspaper received an anonymous letter calling for EnCana to stop flowing the natural gas containing deadly hydrogen sulphide through the area.

Brian Lieverse, EnCana's community relations adviser in Dawson Creek told the Globe and Mail in a telephone interview the Calgary, Alberta, company had increased security at its facilities in the area and has an undisclosed number of private security firms contracted to monitor the pipeline.