Mr. Nix is a director of SCL Group, a British political and defense contractor, and chief executive of its American offshoot, Cambridge Analytica, which advised the Trump campaign. The firms’ employees, who often overlap, had contact in 2014 and 2015 with executives from Lukoil, the Russian oil giant.

Lukoil was interested in how data was used to target American voters, according to two former company insiders who said there were at least three meetings with Lukoil executives in London and Turkey. SCL and Lukoil denied that the talks were political in nature, and SCL also said there were no meetings in London.

The contacts took place as Cambridge Analytica was building a roster of Republican political clients in the United States — and harvesting the Facebook profiles of over 50 million users to develop tools it said could analyze voters’ behavior.