Islamic militant group Boko Haram had said it aims to establish an Islamic state in Nigeria, a country divided along Christian and Muslim lines.
At least 150 people were killed in attacks attributed to Boko Haram in recent days. Human Rights Watch in a report published Tuesday said the militant Islamic group was responsible for the deaths of more than 250 people in Nigeria during the first three weeks of 2012.
Victoria Nuland, a spokeswoman for the U.S. State Department, said anybody involved in attacks on innocent civilians in Nigeria should be brought to justice. Reconciliation, however, is part of a long-term path for peace, she said.
"(Nigerians) are trying to get their arms around how they can do more, how they can provide greater peace and stability and calm things," she said. "But we are also sending a message, very strongly, to all people of Nigeria to settle their issues peacefully and respectfully of each other's differences."
Nigerian President Goodluck Jonathan has faced criticism that he wasn't taking the threats seriously. Middle East and North African analysts said, despite growing rhetoric, Boko Haram is largely a domestic threat to Nigeria.