UNITED NATIONS, Dec. 13 (Xinhua) -- UN Secretary-General Antonio Guterres has strongly condemned Friday's attack on a secondary school in Nigeria's Katsina State and the reported abduction of hundreds of boys by suspected armed bandits, said his spokesman on Sunday.

The secretary-general called for the immediate and unconditional release of the abducted children and for their safe return to their families, said Stephane Dujarric, the spokesman, in a statement.

Guterres reiterated that attacks on schools and other educational facilities constitute a grave violation of human rights. He urged the Nigerian authorities to bring those responsible for this act to justice, said the statement.

The secretary-general reaffirmed the solidarity and support of the United Nations to the government and people of Nigeria in their fight against terrorism, violent extremism and organized crime, it said.