Nigerian troops were reported to be massing for an assault to try to free hundreds of schoolgirls kidnapped by a militant Islamist group.
The authorities raised their estimate of the number of girls held to 223. A further 53 were said to have fled from the Simbisa forest in the north, where the militants have taken them.
They were sitting exams at a school in the town of Chibok when it was attacked by members of Boko Haram.
Local newspapers said four battalions of troops were stationed at all corners of the forest, backed by fighter aircraft, helicopter gunships and police surveillance helicopters.
A large medical team with mobile clinics and air ambulances had also been sent to the area amid fears of casualties if and when an assault was launched.
Boko Haram, which means "Western education is forbidden", is a violent jihadist group that has extended its sway in parts of Muslim northern Nigeria dramatically in the past two years, in part assisted by weapons smuggled across the Sahara from other Islamist groups and from Libyan stockpiles.
It attacked the Government Girls School in Chibok on April 14 under cover of darkness.
The boarding houses were swelled by girls sent for their exams from more remote locations, partly for fear of Boko Haram attacks there.
That also contributed to the widely criticised government response, when widely varying figures were given for the number of victims.
On Saturday, the state police commissioner, Tanko Lawan, said even his new figure of 276 kidnapped girls, aged between 15 and 18, might not be "exhaustive", since there was no definitive roll of which girls were in the school at the time.
Nor was it clear that all the girls are in the forest. The Borno-Yobe People's Forum, a local group, claimed some girls had been forced into marriage in mass weddings with their abductors, who had paid a notional bride price of 2000 naira each, or about $16. It cited contacts who live in the forest.
Some girls had also been taken across national borders to Cameroon and Chad, it said.
"By all means, let's get the support we need from global players," said a former World Bank vice-president, Obiageli Ezekwesili. She was speaking at a sit-in protest organised by dozens of mothers and women in Abuja in support of the release of the girls.
"What these women are saying is that they want their daughters freed," added Ezekwesili.
One Nigerian senator from the area, Ahmad Zanna, told local media he had repeatedly given the authorities information on the girls' whereabouts only for them not to take action until the captives had already been moved on.