NEW : Talks collapse between President Robert Mugabe , opposition `` Darkest day of our lives , '' says MDC leader Morgan Tsvangirai . The Zimbabwean president has been in power for 27 years and is the country's longest-serving leader. Once-prosperous nation facing its worst economic and humanitarian crisis .
NEW : Talks collapse between President Robert Mugabe , opposition `` Darkest day of our lives , '' says MDC leader Morgan Tsvangirai . Mugabe said Monday 's meeting is final one ; will form government without MDC . Once-prosperous nation facing its worst economic and humanitarian crisis .