Seven contractors that were kidnapped by gunmen in southern Nigeria have been released four days after they were abducted.

The seven, including three Australians and a South African, were abducted in the outskirts of Calabar, the capital of Cross River State in the Niger Delta.

Cross River State Commissioner said the seven were released ‘unhurt’ on Sunday.

Australian mining and construction firm Macmahon Holdings Ltd, where the kidnapped are employees, however said in a statement that five of the seven had been injured, two seriously.

Kidnappings of foreigners are a common occurrence in the region which holds most of the OPEC member’s crude oil and contributes about 70 percent of national income.