Two First Nations in British Columbia's southern Interior that had been part of a court challenge against the Trans Mountain pipeline expansion have reversed course and signed deals with the Crown corporation.

The Upper Nicola Band near Merritt and Stk'emlupsemc te Secwepemc near Kamloops dropped out of the Federal Court of Appeal litigation, leaving four B.C. First Nations to fight the case.

The Upper Nicola says in a joint news release with Trans Mountain on Friday that its deal represents a "significant step forward" toward addressing environmental, archeological and cultural heritage concerns.

It says the agreement provides resources to support its active involvement in emergency response and monitoring while helping avoid and mitigate impacts on the band's interests and stewardship areas.

A news release from Stk'emlupsemc te Secwepemc says its leadership determined an agreement could be used to protect its cultural, spiritual and historical connections to the land.

Trans Mountain spokeswoman Ali Hounsell says the two bands dropped out of the challenge last week after continued discussions with the corporation.