Armenian separatists in the breakaway region of Nagorny Karabakh said on Monday 15 more of its fighters have been killed in a flare-up of a territorial dispute, bringing the death toll to 39 as the fighting entered a second day. World leaders have urged a halt to the fighting between Azerbaijan and the Armenian rebels after clashes erupted on Sunday, raising the spectre of an all-out conflict that could draw in regional powers — Russia and Turkey. Ex-Soviet Armenia and Azerbaijan have been locked since the early 1990s in a…