Lagos, Nigeria (CNN) -- Four Shell contractors -- three Britons and a Colombian -- have been kidnapped in Nigeria, a police spokeswoman said Tuesday.
The abductions in the oil-rich Niger Delta happened after attackers ambushed a bus in which the four were traveling, according to Rita Inoma, a police spokeswoman in Port Harcourt, Nigeria.
The ambush killed a police constable and wounded a driver, she said.
The bus was traveling from Port Harcourt, which is southeast of the Nigeria capital, Lagos, to Afam, Nigeria, Inoma said.
Authorities have recovered the bus and continue to investigate.
The Movement for the Emancipation of the Niger Delta (MEND), which is known for its kidnappings of oil workers in the region, announced Tuesday that it had no involvement in the abduction 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.