Officials at a Calgary-based gas company say crews have closed a leak caused by the third attack on its sour gas infrastructure in northeastern B.C.

EnCana workers injected cement into a well Sunday night to seal the leak at a wellhead near Tomslake, south of Dawson Creek. The explosion was discovered Friday in an isolated area about 1,200 kilometres northeast of Vancouver.

It was the third attack on EnCana's sour gas facilities in northern B.C., in the last month.

The RCMP's anti-terrorism unit and explosives investigators were waiting until the leak was sealed before starting work at the site.

The Mounties believe the explosions were set by someone who knows the local area and that they're linked to a threatening letter sent to local media last month.