Women displaced as a result of Boko Haram attacks in the northeast region of Nigeria, sit together at a camp for internally displaced people in Yola, Adamawa State, January 13, 2015. [Photo/Agencies]

UNITED NATIONS - The UN Security Council condemned the recent escalation of attacks by Boko Haram on Monday, in its first formal reaction to the activities of the Nigerian extremist group that seized the world's attention last year with the kidnapping of 276 schoolgirls.

In a presidential statement approved by all 15 members, the council expressed deep concern that Boko Haram's activities are undermining peace and stability in central and west Africa.

The Security Council has previously responded to specific terrorist acts by Boko Haram, including the abduction of 276 schoolgirls in Chibok last April, with press statements that do not become part of its official record. This was the first presidential statement, which does become part of the council record and is second in importance to a council resolution.

The statement comes on the eve of Tuesday's meeting in Niger's capital, Niamey, to discuss the regional response to the threat posed by the Islamic militant group, which is expected to include military action.

The council welcomed the meeting and urged regional countries to undertake planning to put into operation a "sustainable, viable and effective" Multinational Joint Task Force to conduct military operations against Boko Haram. It also welcomed last Friday's vote by Chad's National Assembly which authorized Chadian troops and security forces to assist Cameroonian and Nigerian soldiers in the fight against Boko Haram terrorists.

The Security Council demanded that Boko Haram immediately halt all hostilities, disarm and demobilize. And it demanded the immediate release of all those held captive by the group, including the 276 schoolgirls seized in April.

The council warned that some acts by Boko Haram "may account to crimes against humanity" and stressed that those responsible for violations of international human rights and humanitarian law must be held accountable.