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Police experts at the scene of a bombing near an EnCana sour gas line outside of Dawson Creek, B.C., in October. ((CBC))

A fourth explosion has occurred at an EnCana Corporation natural gas facility in northeastern B.C, just east of Dawson Creek.

RCMP said EnCana gas line workers discovered a partially destroyed metering shed on Sunday at a wellhead near the community of Tomslake.

Investigators said the damage was the result of what appeared to be a deliberate attack similar to three other blasts that occurred at Encana operations in October.

The first blast on Oct. 11 was beside a sour gas line about 50 kilometres east of Dawson Creek, B.C. The second occurred Oct. 16 along a pipeline off Highway 2, about half a kilometre from the provincial boundary with Alberta.

The third blast occurred on Oct. 31, about 12 kilometres northwest of Tomslake, B.C., near the Alberta border.

Many people in the area believe the explosions might be linked to a threatening letter sent to a local newspaper demanding that companies operating sour gas wells and pipelines in the area stop their operations.

Many critics of sour gas development fear the gas, which can be fatal if too much of it is inhaled, poses a danger to nearby residents.

The explosions are being investigated by Canada's anti-terror squad.

With files from The Canadian Press