"Though some countries may oppose it, we’ll raise the issue of Pakistani genocide in Bangladesh during the Liberation War in the international forum," he said.
He made the statement when he met Prime Minister Sheikh Hasina at her office.
PM's Press Secretary Ihsanul Karim briefed reporters after the meeting.
Bangladesh observes March 25 as National Genocide Day and is trying to get international recognition for it.
Sheikh Hasina recalled that the Pakistani occupation forces launched the genocide in Bangladesh on March 25 in 1971.
"Over three million people were killed, while two lakh mothers and sisters lost their honour to Pakistani occupation forces and their local collaborators," she said.
Sheikh Hasina said Father of the Nation Bangabandhu Sheikh Mujibur Rahman rehabilitated the mothers and sisters who were violated during the Liberation War.
The press secretary said the Prime Minister and the UN under-secretary general also discussed the Rohingya issue.
He said Adama Dieng described Myanmar's atrocities on Rohingyas as a genocide and renewed the UN support to Bangladesh on the issue. "The perpetrators of the genocide must be brought to justice," he said.
The UN under-secretary general urged the international community to mount further pressure on Myanmar to bring back its nationals from Bangladesh as it cannot solve the (Rohingya) problem alone.
Adama Dieng said the UN wants repatriation of the Rohingyas to their homeland of Rakhaine state and there will be peaceful and inclusive society.
The UN under-secretary general highly praised Prime Minister Sheikh Hasina for giving shelter to over one million Rohingyas in Bangladesh.
The Prime Minister said the Rohingyas outnumbered the local people of Cox's Bazar. "As a result, the local people are suffering a lot," she said.
Highlighting various steps for the welfare of the Rohingyas, Sheikh Hasina said the government is developing an island for their temporary shelter.
She thanked the international community for extending their helping hand on the Rohingya issue.
While talking about terrorism and militancy, the Prime Minister said a few incidents took place in the country, but the government tackled those with an iron hand.
She said the government is exchanging views with a cross-section of people, including teachers, students, public representatives, religious leaders, to create mass awareness against the menace of terrorism and militancy.
Adama Dieng mentioned outstanding leadership of three female leaders in the world. They are Bangladesh Prime Minister Sheikh Hasina, German Chancellor Angela Markel and New Zealand Premier Jacinda Ardern.
The UN under-secretary general highly praised Sheikh Hasina for ensuring women empowerment in the country. "You're a symbol of women empowerment," he said.
Adama Dieng hoped that Bangladesh will achieve sustainable development goals like MDGs under the leadership of Sheikh Hasina.
He also remembered Father of the Nation Bangabandhu Sheikh Mujibur Rahman terming him a man of peace. "You're materialising Bangabandhu's dream," he said.
About the massacre in two mosques in Christchurch of New Zealand, the Prime Minister said the members Bangladesh National Cricket Team narrowly escaped the carnage.
Both the Prime Minister and the UN under-secretary general praised the steps taken by the New Zealand premier after the massacre that left 50 people dead and scores of others injured.
Chief Adviser to Save and Serve Foundation Syed Nazibul Bashar Maizbhandari, MP, PM's Principal Secretary Md Nojibur Rahman and Military Secretary Major General Mia Mohammad Zainul Abedin were present.