London: Four employees of energy giant BP were missing following the attack on In Amenas gas plant in Algeria, firm`s CEO Bob Dudley said, and added that he feared for their lives.
Fourteen employees were safe and accounted for, but four were untraceable.
In a statement issued on Saturday, Dudley said, "While the situation has evolved, it may still be some time before we have the clarity we all desire.
"While not confirmed, tragically we have grave fears that there may be one or more fatalities within this number.
"Our focus remains on our colleagues who we have not yet been able to locate and on supporting their families through a time of agonising uncertainty.
"BP is a company that cares about its people -- this is a difficult and sad time for us all."
British Petroleum in a statement said it was doing everything it could to support the efforts to locate its employees, "working with the relevant British and Algerian government authorities and agencies".
In Amenas is a joint venture gas project run by the Algerian state oil and gas company Sonatrach, Norway`s Statoil and BP.
BP said that it had about 56 employees in Algeria during the attack and over 25 of them had been evacuated.
At least 19 hostages and 29 Islamist militants have been killed in the four-day-old hostage crisis that gripped the natural gas complex in the middle of the Sahara desert.