Amina Mohammed, the new deputy UN secretary-general, will formally take office on Tuesday, UN spokesman Stephane Dujarric said.

"After that, she will speak at the (UN) Economic and Social Council in her first official engagement with that body, followed by a short encounter with the press," Xinhua news agency quoted Dujarric as saying.

Mohammed, who was appointed by Antonio Guterres on December 15, 2016 as his deputy, was supposed to assume office on January 1, when Guterres took office as the new UN secretary-general.

However, Nigerian President Muhammadu Buhari requested her to complete some ongoing responsibilities, as the Nigerian minister of environment, that she was handling at that time, thus leading to her delayed move to assume her new role at the United Nations.

The office of the UN deputy secretary-general was formally established by the UN General Assembly in 1997 to handle many of the administrative responsibilities of the secretary-general.

As the fifth deputy secretary-general, Mohammed will help to manage the UN Secretariat operations, and ensure inter-sectoral and inter-institutional coherence of activities and programmes.

She will also support the Secretary-General in elevating "the profile and leadership of the UN in the economic and social spheres, including further efforts to strengthen the UN as a leading centre for development policy and development assistance."

Amina served as UN under-secretary-general and special adviser to former UN Secretary-General Ban Ki-moon on Post-2015 Development Planning.

She was instrumental in bringing about the 2030 Agenda for Sustainable Development, including the Sustainable Development Goals (SDGs), which serves as the blueprint for the global development efforts for the years between 2015 and 2030.