ADDIS ABABA (Reuters) - Ethiopa’s Prime Minister Abiy Ahmed, who won the 2019 Nobel Peace Prize, has sent troops into northern Tigray state whose leaders he accuses of treason, triggering a conflict with implications around the Horn of Africa.Africa’s second largest nation, with 115 million people, was already suffering from COVID-19, a locust plague and ethnic clashes that have uprooted hundreds of thousands in the last two years. Now the Tigray conflict has killed hundreds of combatants, sent more than 10,000 refugees fleeing to Sudan and interrupted aid operations for more than half a million people reliant on food aid and other emergency assistance. Non-essential United Nations’ staff and others have pulled out. HORN OF AFRICA SECURITY Tigray borders both Sudan and Eritrea, which fought a 1998-2000 war with Ethiopia that killed tens of thousands in trench warfare and minefields. Despite the 2018 peace deal, Eritrea’s President Isaias Afwerki remains hostile to the TPLF and there are fears Asmara may become sucked in to back Abiy. Ethiopia’s military is the most effective in the Horn of Africa, which borders the Suez Canal, one of the world’s busiest shipping routes. It plays a big role in an African Union (AU) force combating al Qaeda-linked militants in Somalia, which may be affected if it has to divert resources to Tigray.