The abducted workers were seized in an attack on an oil field last week . They are from the Philippines , the Czech Republic , Austria , Bangladesh and Ghana . Militants have carried out a series of attacks on oil fields in recent weeks .
The abducted workers were seized in an attack on an oil field last week . They are from the Philippines , Bangladesh , Austria , the Czech Republic and Ghana . Militants have carried out a series of attacks on oil fields in recent weeks .