The Nigerian President has cancelled a planned visit to the village from which nearly 300 girls were kidnapped due to security fears.

The visit was to be Goodluck Jonathan's first visit to Chibok, the village from where more nearly 300 schoolgirls were abducted by Boko Haram rebels a month ago.

"The President was planning to go but security advised otherwise on the visit" said the source of the last-minute decision to cancel.

Instead, Mr. Jonathan is to fly direct from the capital - Abuja - to Paris for a regional summit to discuss Boko Haram and wider security issues.

The cancellation of the visit to Chibok is likely to disappoint relatives of the girls - who have already expressed their anger at the government's slow response to the crisis and the armed forces' failure to rescue the girls.

Boko Haram's leader last week threatened in a video to sell the girls and young women into slavery unless the government freed rebels being held - the President said he would not do so.

Mr. Jonathan has now accepted international help in the search following international outrage at the kidnappings.

The US has started flying aircraft over the area where it is suspected the girls are being held - residents of Chibok say they have not seen any planes.

The girls believed to be being held in the vast Sambisa forest which begins 20 miles from Chibok.

"Tragically and unacceptably slow"

Mr. Jonathan and his government have been widely criticised for their slow response to the kidnapping on April 14th, which saw 276 girls abducted by militants. A total of 223 are still missing.

But they were forced to act in the face of a social media and street protests that won global support and attracted the attention of foreign powers, who have now sent specialist teams to help in the rescue effort.

In the US, the chairman of the Senate Committee on Foreign Relations said Nigeria had been "tragically and unacceptably slow" to tackle the crisis.

"I have called on President (Goodluck) Jonathan to demonstrate the leadership his nation is demanding" Democratic senator Robert Menendez said.

Department of Defence official Alice Friend said Nigeria, which has previously resisted outside help to put down the five-year insurgency, could be "an extremely challenging partner to work with".

"In the face of this sophisticated threat, Nigeria's security forces have been slow to adapt with new strategies and new tactics," she added.

Mr. Jonathan has ruled out a prisoner swap with the extremists, but the government said it remained open to wider talks on ending the insurgency.

Relatives of the missing girls have called for their unconditional release.

"For me, I want these girls released without any negotiations" said Ayuba Chibok, whose niece is among the hostages.

"Even if Boko Haram wants to request something from the government, let them request something else. Let (Shekau) release these girls unconditionally".