(Changes identifying slug for media clients, ** change to text) CAIRO, June 16 (Reuters) - A Libyan militant group appeared to deny reports that a U.S. strike had killed veteran Algerian Islamist Mokhtar Belmokhtar, in a statement published on Twitter. Libya's government said on Sunday that Mokhtar, blamed for a deadly assault on an Algerian gas field and a major figure in insurgencies across **rth Africa, had died alongside other militant leaders.