The President of Nigeria, Umaru Yar'Adua, has appealed for the immediate release of a three-year-old British girl kidnapped by gunmen.
Mrs Hill says her husband was willing to trade himself for Margaret
Mr Yar'Adua has ordered the Nigerian security services to ensure that Margaret Hill is returned unharmed to her family.
The girl's parents said the kidnappers were demanding a ransom.
Margaret Hill was snatched from a car on her way to school in Port Harcourt, in the volatile Niger Delta region.
Officials said that security forces would not resort to violence in order to free the girl.
A statement released by the president's office said "President Yar'Adua... appeals once again for a total cessation of all acts of violence in the region, the release of little Miss Margaret Hill and all other hostages."
"He has directed the security agencies to make every possible effort to ensure that she is returned to her family unharmed and he remains in touch with all efforts being made to secure the girl's release," the statement said.
Her mother, Oluchi, says the kidnappers have threatened to kill Margaret unless her husband takes the girl's place.
Margaret was snatched by gunmen at 0730 (0630 GMT) on Thursday after they smashed a window of the car as it sat in traffic.
The kidnappers telephoned Mrs Hill and said they would free the child but only if her father, Mike, took her place.
Mrs Hill, a Nigerian national, told the BBC that the kidnappers told her to meet them in a town in Bayelsa State in the Niger Delta region, but that neither she nor the police had been able to locate it.
She said they then allowed her to speak to her daughter, who was crying.
"They say I can bring my husband to swap with the baby," Mrs Hill said.
"He wanted to go down for his baby but the police commander told him not to."
Mrs Hill said the kidnappers threatened to kill Margaret if Mr Hill did not come within three hours.
After the deadline had expired, Mrs Hill said Margaret was being fed just "bread and water".
The family says the kidnappers have also asked for money.
Nigerian national police chief Mike Okiro has gone to Port Harcourt, where he held meetings with security officials.
WHO ARE MEND
Formed early 2006
Close links to militant Mujahid Dokubo-Asari's Niger Delta Volunteer Force
Split into two rival groups late 2006
Demand 100% control of Nigeria's oil wealth
Demand release of impeached Bayelsa governor on trial for money laundering
Operate from creeks of Niger Delta
Communicate with media by e-mail
The region's main militant group - the Movement for the Emancipation of the Niger Delta (Mend) - has offered to help find the child.
"We will join in the hunt for the monsters who carried out this abduction and mete out adequate punishment for this crime. We abhor all forms of violence against women and children," the group said in a statement.
The UK's Foreign Office has called for Margaret's "immediate safe release".
The BBC's Alex Last in Lagos says Mr Hill is ill and had been due to fly to the UK for medical treatment.
He says that no hostage has ever been killed by kidnappers in Nigeria and more than 200 have been taken by armed groups in the last 18 months.
Almost all were freed after a ransom was paid.