Signs that Canadian citizens were involved in the attack by hostage-taking Islamist militants on a remote gas plant in Algeria are of great concern to American authorities, U.S. intelligence officials said on Thursday. While Algerian authorities apparently have not yet provided Western governments with cast-iron proof, a senior U.S. intelligence official said: “We’re taking very seriously the reports of the two Canadians’ involvement.” ... Confirmation that Canadian citizens were involved in the attack on the In Amenas facility in the Algerian desert would raise concerns about a worrying nexus between North America and North African militants. At least 38 plant...