In a statement issued on Tuesday, Unicef Nigeria Representative Peter Hawkins said that the fund would work with the Ministry of Education to ensure the safe return of all children to school, Xinhua news agency reported. 

"While we rejoice at the release of the schoolgirls and look forward to their safe return to their families, we reiterate that attacks on students and schools are not only reprehensible but a violation of the right of children to education," he said. 

"Unicef calls on the government of Nigeria to take all measures to protect schools in the country so that children will not be fearful of going to school, and parents afraid of sending their children to school. 

"Schools must be safe places to study and develop, and learning should not become a risky endeavour," he added. 

In an announcement on Tuesday, Zamfara state Governor Bello Matawalle said that the girls, who were abducted from the Government Girls Science Secondary School in the Jangebe town on February 26, were released after a series of negotiations early Tuesday. 

The Governor insisted no ransom was paid for the release of the schoolgirls, adding it was a positive result of the peace accord he initiated. 

Officials said "bandits" were behind the abduction, referring to the groups of armed men who operate in Zamfara state and kidnap for money or to push for the release of their members from jail. 

Also on Tuesday, Hafsatu Anka, one of the abducted victims, told reporters that they were laid in trenches littered with human feces. 

"We saw other people, including women and children, and the father of one of our schoolmates, who had been in the kidnappers' den for three months," Anka narrated. 

"They walked us on foot where some of us got dislocated on their foot. They would pray as Muslims but never allowed us to pray. They fed us with rice, in which they put sand after cooking," the girl added. 

The Zamfara abductions were the second in the country in recent weeks. 

Last month, at least 27 students were kidnapped from a boarding school in Kagara, Niger state. 

They were released on February 17. 

In 2014, 276 schoolgirls were kidnapped by the Islamist Boko Haram terrorists in Chibok town, which drew global attention and condemnation. 

More than 110 of those girls are still unaccounted for, while the remaining either escaped, freed by the military or died.