Lagos, Nigeria (CNN) -- Four Shell contractors -- three Britons and a Colombian -- have been released after being kidnapped a week ago, a police spokeswoman said Tuesday.
The abductions in the oil-rich Niger Delta happened last Tuesday when attackers ambushed a bus in which the four were traveling, according to Rita Inoma, a police spokeswoman in Port Harcourt, Nigeria.
The former hostages were doing well, Inoma said.
It was unclear where the hostages had been held and what prompted their release.
The ambush last week killed a police constable and wounded a driver, Inoma said.
The bus was traveling from Port Harcourt, which is southeast of here, the Nigerian capital, to Afam, Nigeria, Inoma said.
The Movement for the Emancipation of the Niger Delta (MEND), which is known for its kidnappings of oil workers in the region, had announced after the abduction that it had no involvement in the kidnappings of the Shell contractors.
The militant group has demanded a fairer distribution of the country's oil wealth and for the release of its members imprisoned by the government.
CNN's Christian Purefoy contributed to this report.