MICHELLE NICHOLS UNITED Nations human rights chief Michelle Bachelet has agreed to an Ethiopian request for a joint investigation in the country's northern Tigray region, where Bachelet says possible war crimes may have been committed. Fighting between government troops and the region's former ruling party, the Tigray People's Liberation Front (TPLF), has killed thousands of people and forced hundreds of thousands from their homes in the mountainous region of about 5 million. The United Nations has raised concerns about atrocities being committed in Tigray, while U.S. Secretary of State Antony Blinken has described acts carried out in the region as…