AFRICAN Union envoys arrived in Ethiopia hours before an ultimatum was to expire for Tigrayan forces to surrender in a war that has shaken the northern region and killed thousands of its fighters according to one report. Prime Minister Abiy Ahmed's government has set a 72-hour deadline for the Tigray People's Liberation Front (TPLF) to lay down arms or face an assault on their highland capital Mekelle, home to half a million people. The deadline was due to run out on Wednesday evening. Large numbers have died and there has been widespread destruction in aerial bombardments and ground fighting since…