The U.S. Monday added Igor Sechin, a Putin ally and head of state-controlled oil giant , to its sanctions list, complicating the delicate dance U.S. and European energy giants have had to engage in amid the standoff between the West and Moscow. The most exposed company is U.K. oil company PLC, which has a 19.75% stake in Rosneft. Last year, it sold its stake in its previous Russian joint venture for $11.8 billion in cash plus shares in the state-controlled oil giant. Mr. Sechin owns 0.13% of Rosneft, making him the company’s third-largest shareholder after the Russian state and BP. BP also gained a seat on Rosneft’s nine-member board, currently held by BP Chief Executive Bob Dudley. Under the terms of the U.S. sanctions, BP wouldn’t be barred from dealing with Rosneft, though Mr Dudley, an American citizen, would be unable to have direct business dealings with Mr. Sechin. […]