YEREVAN, Armenia — Leaders of Azerbaijan and Armenia brushed off the suggestion of peace talks Tuesday, accusing each other of obstructing negotiations over the separatist territory of Nagorno-Karabakh, with dozens killed and injured in three days of heavy fighting. In the latest incident, Armenia said one of its warplanes was shot down by a fighter jet from Azerbaijan’s ally Turkey, killing the pilot, in what would be a major escalation of the violence.