The BP-backed chief executive of TNK-BP, its Russian oil venture, has warned foreign staff in an email that he and all other foreign employees could be forced to leave Russia by the end of the month because Moscow authorities had not renewed work visas.

As pressure increased on BP amid a bitter corporate war with its Russian partners, Robert Dudley told about 100 foreign employees at TNK-BP that “all expatriate staff may be affected” by the visa problems, “including myself, and may have no choice but to leave Russia by or before the end of July”.