Knife River rises on report Starboard urges co to explore sale

** Shares of construction materials and contracting service provider Knife River Corp (KNF.N) rise 1.5% to $52.20 in extended trading

** Activist investor Starboard has taken a significant stake in Knife River, with plans to push the company to improve its margins or explore a sale, the Wall Street Journal reports, citing people familiar with the matter

** Starboard wants the company to evaluate strategic alternatives including a potential sale, as it believes its business has a high barrier to entry and could be attractive to potential suitors, according to the WSJ

** Starboard also wants Knife River to commit to narrowing the gap between its EBITDA margins and those of its peers in the next few years, the WSJ reports

** Knife River and Starboard did not immediately respond to Reuters' requests for comment. Reuters could not independently verify the report.

** As of last close, KNF was down 26.9% year to date