JOHANNESBURG (Reuters) - South African diversified resources group Exxaro reported an 11 percent rise in first-half earnings on Thursday as it lifted coal exports on the back of a weaker rand. Exxaro's headline earnings per share came in at 793 cents for the six months to end June compared to 714 cents in the same period last year. Exxaro, South Africa's second-largest coal producer, while exports had risen, trading conditions remained challenging and export prices in the period had fallen to $68 per tonne from $82 last year. "Due to the international oversupply of both thermal and coking coal, coal prices are expected to remain under pressure for the rest of the year as there are still signs of additional supply coming onto the market," the company said.