In a sign of mounting international concern about fighting in South Sudan, Britain said on Thursday that it had dispatched an airplane to evacuate British nationals as clashes were reported to have spread following claims of an attempted coup. The Foreign Office said that around 150 of the estimated 500 Britons in the newly created country had been in touch with British officials, many of them wanting to leave the country. The developments came a day after the South Sudanese Army said that it had lost control of a town in the north of the country. South Sudan declared its independence in July 2011, after years of struggle to break away from the Arab-dominated north of Sudan. But in the past few days, President Salva Kiir has accused his former vice president, Riek Machar, of attempting to overthrow him — a charge Mr. Machar denied on Wednesday. […]