Nigerian police are offering a $300,000 reward to help the search for 276 missing schoolgirls kidnapped by militants last month.
The Nigeria Police Force says the award will go to anyone who provides "credible information that will lead to the location and rescue" of the students, who were abducted from a secondary school in the village of Chibok, in Borno state.
Numbers to call are posted on the Nigerian police website. The force says any information it receives will be treated with "utmost confidentiality."
The leader of Islamist militant group Boko Haram claims responsibility for kidnapping the girls and says the group intends to sell them.
The United States said Tuesday it will send intelligence and law enforcement experts to Nigeria to assist in the rescue effort.
In an interview with ABC television, President Barack Obama said this may be the event that mobilizes the world to do something against what he calls a "horrendous organization."
Boko Haram is blamed for thousands of deaths in bombing and shooting attacks during the past five years. Two recent bombings at a bus station near the capital, Abuja, killed 100 people.
The militants say they are fighting to establish a strict Islamic state in Muslim-majority northern Nigeria.
Many Nigerians accuse the government of not doing enough to free the girls. President Goodluck Jonathan said he has ordered his top security officials to do all they can to secure the girls' release.