ReutersRussian oil giant Lukoil has lost yet another top executive under mysterious circumstances as its vice president died “suddenly” at the age of 53, adding to a spate of deaths of figures linked to the gas and oil industry in the country. The company announced the death of Vitaly Robertus in a brief statement Wednesday, expressing “deep regret” over his death but providing no further details on the manner in which he died.His passing comes after a string of bizarre deaths at the company. Mo