The statement read, "President Buhari joins the Borno State government, parents of the children and Nigerians in commemorating the fourth anniversary of the sad incident, praying that the event at the daughters' school today will go well".
Boko Haram, which seeks to create an Islamic state in northeast Nigeria and split into two main factions in 2016, has killed more than 20,000 people since it launched its insurgency in 2009.
The UN agency noted that four years on, more than 100 of the Chibok girls had yet to be returned to their families.
The Imam of Falomo Police Mosque, Imam Tajudeen Adebayo, during the interfaith prayers, thanked Allah for those that were released and prayed that the remaining girls would also be rescued.
She became pregnant and "now lives with her young son in an IDP (displaced persons) camp, where she has struggled to integrate with the other women due to language barriers and the stigma of being a "Boko Haram wife", UNICEF said.
In a statement released on the eve of the April 14, fourth anniversary of the kidnap of over 200 schoolgirls in Chibok, Borno State, the United Nations agency also said more than 1,000 children had been abducted and 1,400 schools destroyed by the terrorists in the region since 2013.
"The President urges the parents to keep their hopes alive on the return of their daughters, noting that the recovery of more than a 100 of the girls that were kidnapped through the Federal Government's determined effort should give confidence that all "hope is not lost".More news: Salah, De Bruyne lead 6-man PFA Player of the Year shortlist
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In May 2017 another 82 girls are released in exchange for five Boko Haram commanders as part of the same talks.
"What happened in Chibok should have served as a wake-up call to the Nigerian government".
"To us as a community and even the parents of these missing girls, four years of waiting in anticipation of seeing your missing child return home can be very traumatizing".
So far, the current administration has been able to secure the release of 103 of them while a few others have been rescued.
The President re-affirmed that the government remained focused and determined to see the girls return to their homes.
"We have heard several rumor that some of the girls are dead; to that effect the federal government should come clear with credible information on the true situation so that some of the parents whose daughters may have died, can put their minds to rest rather than continuing to suffer the trauma they have suffered all this four years".
Boko Haram factional leader Abubakar Shekau claims responsibility in a video released on May 5 and vows to sell the girls as slave brides.