Nigerian police have said Boko Haram militants are holding 223 girls of the 276 seized from their school in the country's northeast, revising upwards the number of youngsters abducted.

School and government officials in the northeastern state of Borno had previously given lower figures.

The girls were abducted nearly three weeks ago in the town of Chibok.

Gunmen believed to be Islamist fighters stormed the girls' boarding school.

They forced them from their dormitories onto trucks and driving them into the bush after a gun battle with soldiers.

Borno state police commissioner Lawan Tanko said his officers and other security agencies revised the figure.

The move came after intensive and extensive investigation, consultations and collation of figures from parents and the school. 

Mr Tanko said: "So far, we have a comprehensive list of 276 girls abducted from the Government Girls Secondary School in Chibok on 14 April and out of this figure, 53 were able to escape and return."

"We have documented all the 53 girls that escaped."

A spokesman for Borno state governor said in the days after the abduction that 129 girls were taken and 52 escaped, leaving 77 with the abductors. 

But the school principal disputed the figures, maintaining that 230 girls were kidnapped, out of which 43 escaped while 187 were taken away. 

Mr Tanko blamed the discrepancy on the fact that the students were from various schools in the area and had been transferred to Chibok to sit their final exams because of Boko Haram violence elsewhere in the state.

Student records were also burnt in a fire that destroyed a large part of the school after the attack, he added.

The girls' abduction has triggered global outrage and prompted protests in a number of Nigerian cities, calling on the government to secure their release.

Nigeria's information minister, Labaran Maku, said that President Goodluck Jonathan chaired a top-level meeting with the military and security chiefs to review progress on a possible rescue mission.

The government has denied charges from the girls' families that they have mishandled the situation.

Mr Maku said "extensive and intensive aerial surveillance" had been carried out around Chibok and the border regions.

Search teams were also combing "all reported places that the girls might have been taken to".