The United States will send a team of military and police experts to Nigeria to help find more than 200 kidnapped schoolgirls, amid a growing wave of outrage over their abduction.
US Secretary of State John Kerry said Tuesday he had made the offer in a phone call to Nigeria's President Goodluck Jonathan, which the Nigerian leader accepted.
Washington has also offered to set up a coordination cell at its embassy in Abuja with US military personnel, law enforcement officials as well as experts in hostage situations.
"President Goodluck Jonathan was very happy to receive this offer and ready to move on it immediately," Kerry told reporters, after talks with EU foreign policy chief Catherine Ashton.
"We are immediately engaging in order to implement this," Kerry added.
In Abuja, Jonathan accepted the offer which his office said would "include the deployment of US security personnel and assets to work with their Nigerian counterparts in the search and rescue operation."
The Nigerian leader said his country's "security agencies, who were already working at full capacity to find and rescue the abducted girls, would appreciate the deployment of American counter-insurgency know-how and expertise in support of their efforts."
The issue was also set to dominate talks between Kerry and President Barack Obama later Tuesday.
The leader of the Islamist militant group Boko Haram claimed responsibility for the abductions in a video obtained by AFP Monday.
Although the girls, aged between 16 to 18, were kidnapped from their boarding school some three weeks ago in northeastern Nigeria, the release of the video has pushed the abductions to the forefront of US television news.
Lawmakers have called on the Obama administration to do all it can to help free the girls, and a Twitter hashtag #BringBackOurGirls has gone viral.
Some 200 protesters gathered Tuesday outside the Nigerian embassy in Washington to demand the country take robust action to rescue the girls from the hands of the Islamist militants.
Chanting "bring back our girls" and "no more abuse," they called upon Jonathan to show what one speaker called the "testicular fortitude" to resolve the crisis.
"This is something that touched me... Kids of our generation do care about something and stand up for something," said Tifawni Haynes, 18, a high school student from Washington.
She said the US should use its influence to get Abuja to act: "Americans needs to say, these are your people, you need to do something about them."
Abubakar Shekau, the Boko Haram leader, said the extremist group was holding the schoolgirls abducted from Chibok on April 14 as "slaves" and threatened to "sell them in the market."
Eight more schoolgirls were kidnapped by gunmen from the village of Warabe in Nigeria's embattled northeast, near Chibok, residents said Tuesday.
Jonathan's government has so far been powerless in the hunt for the girls, but had been reluctant to accept any outside help.
"We remain deeply concerned about the welfare of these young girls, and we want to provide whatever assistance is possible in order to help for their safe return to their families," Kerry said.
State Department officials said the US had long been involved in helping Nigeria improve its criminal justice system, and in the past year had given some $3 million to the country in law enforcement assistance.