Niger's president said suicide bombers who carried out simultaneous attacks on a military installation and a French-run uranium mine came from southern Libya.
Mahamadou Issoufou said the death toll was now 35, including 24 soldiers, one employee of French nuclear giant Areva, and 10 terrorists.
He spoke alongside the chief executive of Areva, Luc Oursel, who was returning from the town of Arlit where he had gone to comfort victims of the attack on the Areva-run mine.
Both that attack and the one in Agadez that began at dawn on Thursday were claimed by the Movement for Oneness and Jihad in West Africa and by Algerian terrorist Moktar Belmoktar.
Mr Issoufou said he had contacted the G8 group of nations to urge action to avoid the "Somalisation of Libya".