ADDIS ABABA (Reuters) - Ethiopia’s parliament has appointed a new head of Tigray region, Prime Minister Abiy Ahmed said on Friday, as federal forces pressed a military offensive against leaders of the northern region whom the government accuses of treason and terrorism. The announcement came a day after parliament stripped Tigray president Debretsion Gebremichael - who was elected in September and chairs the Tigray People’s Liberation Front (TPLF) - of immunity from prosecution.