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The American family of one of Libya's top oil officials said Tuesday he has been missing in the chaotic country for five days.

Libya OPEC Governor Samir Salem Kamal was last seen taking the elevator toward the parking lot at the Ministry of Oil in the capital Tripoli, his family told NBC News.

They became worried when he had not returned home by Friday. His car was no longer at the ministry and has not yet been found, they said.

"It is very, very worrying," said one family member who asked not to be identified for fear it may jeopardize Kamal's return. "We have no indication whether he’s alive or dead. He has a heart condition and needs medication."

An undated image of Libya OPEC Governor Samir Salem Kamal. Family

The country has been mired in chaos since the overthrow of Moammar Gadhafi in 2011. The internationally recognized administration of Prime Minister Abdullah al-Thinni now rules from the east after a rival faction called Libya Dawn took power in the capital.

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Both the state-run National Oil Corporation and Tripoli's oil ministry confirmed to Reuters that Kamal was missing. Neither provided further details.

Kamal has been OPEC governor in Libya — a country with the world's ninth largest oil reserves — since March 2012. According to the family, he has also been a director in the planning department of the country’s Ministry of Oil since November 2011.

He is a Libyan national, but most of his family members are based in Washington, D.C., and have American citizenship. They allege that officials connected to Tripoli’s fragile government have hinted they know the whereabouts of their father but have provided no information to support this.

After requesting help from State Department and Libyan officials — with little response, they say — the family say they do not know where to turn. NBC News reached out to OPEC and the State Department on Tuesday without response.

According to a report by Reuters on Tuesday, Kamal’s official title within the fractured country is currently unclear.

Thinni's government did not nominate him for the last OPEC meeting in Vienna in November, the news agency reported. But OPEC's website still lists him as its representative, and according to Reuters officials in Tripoli say he still holds that position.

The oil ministry in Tripoli is run by an oil minister from the non-recognized government who was denied a visa by OPEC to attend its Vienna meeting.

In-Depth

- Alexander Smith

Reuters contributed to this report.