A three-year-old was kidnapped Thursday by gunmen in southern Nigeria; they now threaten to kill her unless she is replaced by her father, the mother says.

Margaret Hill, 3, is the daughter of expatriate oil worker Michael Hill and Nigerian national Oluchi Hill. The little girl was snatched by armed men on Thursday, as she was being taken to school in the oil city of Port Harcourt

The gunmen smashed a window of the car as it waited in traffic and kidnapped the toddler.

Mrs. Hill told BBC that the kidnappers called the same day and demanded a meeting in a town in the Niger Delta, Bayelsa State. They allowed Mrs. Hill to talk to her daughter, who was crying.

She said neither she nor the police had been able to find the town and that the kidnappers had threatened to kill Margaret if she was not there for the meeting within three hours. They did not call back.

Mrs. Hill also told BBC that the kidnappers told her they would return Margaret if the girl’s father took her place. “They say I can bring my husband to swap with the baby,” she said. “He wanted to go down for his baby but the police commander told him not to.”

The UK's Foreign Office has called for the “immediate safe release” of the girl.

According to media reports, there are a large number of armed groups in the Niger Delta, who kidnap individuals and return them, usually quickly and safely, once ransom is paid. The kidnappers usually take foreign oil workers.