Islamic State (IS) militants are said to have kidnapped nine foreign oil workers in a raid in Libya, when they reportedly beheaded eight guards.
Four Filipinos, an Austrian, a Bangladeshi, a Czech and a Ghanaian were taken with an unidentified ninth foreigner, Austrian officials say.
The foreign ministry in Vienna said IS had attacked the al-Ghani oil field.
A Libyan army spokesman told the BBC the field 700km (440 miles) south-east of Tripoli had been attacked on Friday.
One oil worker died of a heart attack after seeing the beheadings, he added.
The foreigners were working for oilfield management company Value Added Oilfield Services (VAOS) at the field.
VAOS said it did not know which militants had carried out the attack or where the oil workers had been taken.
It insisted that none of its employees had "died or were physically harmed in the attack".
Analysis: Rana Jawad, BBC News, Tripoli
Libya is getting more dangerous by the day. As with the attack on the Mabruk oil field last month, the guards at al-Ghani were brutally killed, the foreigners were taken, and the local staff allowed to leave.
The only information available is from shell-shocked witnesses lucky enough to have been allowed to live. We are told that the assailants did not linger around.
These latest attacks do not bear the hallmarks of militias driven by local grievances or political rivalry, as seen in the past.
Instead, their wider aim appears to be to instil fear, mark territory and demonstrate the capacity to wreak havoc.
Confirming that four of the missing workers were their nationals, the Philippines said it brought to seven the number of Filipinos now missing in Libya.
'Burn, destroy and steal'
A spokesman for Libya's National Oil Corporation, Mohamed Al-Harari, told the BBC he could not confirm the abduction of foreign oil workers.
However, he added that local oil workers at the field had been held for two hours before being released.
"These oil workers have said that the gunmen kidnapped a number of foreigners," he said.
Libyan army spokesman Ahmed al-Mesmari told the BBC he had "no information or verified reports" about the missing foreigners.
Speaking after a string of attacks on fields in recent weeks, he said militants aimed to do maximum damage.
"The attackers don't want to control the oil fields, that's not their aim - it seems their aim is to burn, destroy and steal whatever they can," he told the BBC.
After burning the biggest oil storage tank in the al-Ghani field, they headed for another oil field, al-Zoueitina, but were repelled, he added.
Last week, Islamist militants were reported to be behind an attack on two oil fields in Bahi and Mabruk.
Rival militias have been fighting for control in Libya since Muammar Gaddafi was ousted in 2011.