A jihadist group in Libya on Monday released a video showing a kidnapped Tunisian embassy staffer pleading with authorities in Tunis to negotiate with his captors.
The hostage, Mohamed ben Sheikh, is shown crying during the five-minute video as he calls on Tunisia's president to help rescue him.
He is being held by a largely unknown group calling itself Shabab Al-Tawhid.
"Mr President, why do you want to deprive me of life?.. There are no negotiations, they will not release me," he said.
"Mr President, negotiate with them. I want to return to Tunisia. They can kill me at any time."
The video was posted on social networking sites.
The hostage's sister, interviewed on Tunisian radio, confirmed it was her brother speaking and said she feared for his life.
"We won't be able to wait any longer," she said, adding that she had been in contact with the Tunisian authorities.
"When I call them they tell me 'your brother is fine... We are negotiating'."
Mohamed ben Sheikh, who was kidnapped in Tripoli last month, is one of two officials from the Tunisian embassy being held hostage by assailants.
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The video does not mention the other, diplomat Al-Aroussi Kontassi who was seized on Thursday.
Their abductions come during a string of attacks targeting diplomats in the Libyan capital.
Jordan's ambassador to Libya has also been kidnapped and Portugal's embassy was attacked by gunmen.
At the end of the video, the captors, in a message to the Tunisian government, claim: "As you imprison ours, we imprison yours. As you kill ours, we kill yours."
Tunisia's national security council convened on Monday, with President Moncef Marzouki, Prime Minister Mehdi Jomaa and Defence Minister Ghazi Jribi taking part, to examine the security situation in Libya and the case of the two kidnapped Tunisians.
The meeting reviewed the "work of the crisis cell set up by the foreign ministry ... and the efforts made to find a solution," the president's office said.
According to the authorities in Tunis, the group is demanding the release of Libyans jailed for their role in a deadly "terrorist operation" in Rouhia, in northwestern Tunisia, three years ago.
Two army officers were killed in the May 2011 shootout with suspected Al-Qaeda militants.
Diplomats in Tripoli say militias which fought to topple the Moamer Kadhafi regime in the 2011 uprising often carry out kidnappings to blackmail other countries into releasing Libyans they hold.
Libya has been awash with weapons since the end of the uprising that killed Kadhafi and has been gripped by increasing lawlessness.