TOKYO, June 19 (Reuters) - Former U.S. Ambassador to Japan John Roos on Saturday endorsed the continued leadership of Toshiba Corp (6502.T) Board Chairman Osamu Nagayama, who has come under intense pressure to resign amid a deepening crisis at the Japanese conglomerate. Both Nagayama and Roos served as independent directors at Sony Group Corp"s (6758.T) board when the electronic giant emerged from a turbulent earnings period to a sharp recovery. "I am convinced Toshiba"s shareholders will benefit from him continuing to provide his steady hand and strong leadership," Roos said in the statement.