Nigerian President Goodluck Jonathan has ruled out releasing Boko Haram fighters in exchange for the freedom of more than 200 schoolgirls kidnapped by the militants a month ago.
Britain's Africa minister Mark Simmonds, in Nigeria for talks about the international rescue mission, said he raised the issue with Jonathan during a meeting in Abuja.
"He made it very clear that there will be no negotiation with Boko Haram that involves a swap of abducted schoolgirls for prisoners," Simmonds said.
Boko Haram leader Abubakar Shekau suggested in a video released on Monday that he may be prepared to release the girls if Nigeria freed militants held in the country's jails.
Interior Minister Abba Moro immediately rejected the plan, saying that the Islamist group, which has waged a deadly insurgency in northeast Nigeria since 2009, could not dictate terms.
A door appeared to have opened to discussions about the girls on Tuesday when special duties minister Taminu Turaki indicated their freedom could up for discussion. But Simmonds said Jonathan had now ruled that out but was still prepared to fulfil his pledge of talking to the extremists about wider issues.
The rejection of a prisoner swap came as international powers ramped up the search effort, including with the use of US military surveillance drones and manned aircraft.
The Pentagon has deployed the robotic Global Hawk, which flies at high altitude, and the MC-12, a propeller plane heavily used in Afghanistan. Both were "unarmed" and strictly being used for surveillance.
But the data is not yet being shared with the Nigerians because Washington is still working out an agreement to govern the sharing of intelligence.
Washington said freeing the 276 Nigerian girls from Boko Haram is now one of its top priorities.
Robert Jackson, a State Department specialist on Africa, said that Boko Haram "has no regard for human life". He said the Obama administration was boosting Nigeria's law enforcement capabilities, while seeking global sanctions on Boko Haram.
Hawkish Republican senator John McCain said the Pentagon should consider acting unilaterally and sending US special forces in to rescue the girls from the Boko Haram "animals".
Additional reporting by Associated Press