Nigeria's defence minister has hit out at those paying ransoms to kidnappers, saying crowdfunding makes it worse.

Mohammed Badaru Abubakar's comments come as a deadline to pay a ransom for the release of five sisters expired.

They were abducted from their home earlier this month in the capital, Abuja, along with another of their sisters who was later killed.

The case has shocked the country and people have been donating to a crowdfunding initiative.

"We are anxious, everyone is waiting. We just want them back home. All of them [the family] are just praying," Asiya Adamu, a cousin to the sisters, told BBC Hausa on Wednesday.

There has been no word from the family since the deadline expired.

The six sisters, aged from the early teens to 23, were taken hostage in the Abuja suburb of Bwari along with their father Mansoor Al-Kadriyar, who was later released to raise the ransom.

His 21-year-old daughter, Nabeeha, a final year university student, was killed last Friday as a warning that the huge ransom be paid.

But Mr Abubakar said responding to the kidnappers' demands only made them more greedy.

"On crowdfunding, we all know there's an existing law against payment of ransom. So, it is very sad for people to go over the internet, radio asking for donations to pay ransom. This will only worsen the situation," he said.

In this case it had made the kidnappers increase their demands, the minister said.

''We believe we have to stop - as painful as it is. We have to stop responding to payment on ransom. If we stop, over time the kidnapping will not be profitable and they will stop.''

Kidnapping has become rife in Nigeria, with hundreds of people abducted in recent years, largely by criminal gangs who see it as an easy way to make money. It has been particularly bad in the north-west of the country.

There has been an outcry that the insecurity has reached the capital, prompting Abuja's police force to launch a special squad to tackle the kidnapping gangs on Wednesday.

Mr Abubakar said he believed operations against the gangs elsewhere had forced them to move to areas near the capital.

"The security agencies are working very hard to push them out and block the movements and finish them off once and for all."