* Diplomat makes plea in video released by Islamist group
* One of 2 Tunisian diplomats seized in past month
* Libyan Islamists want release of militants jailed in Tunisia
By Feras Bosalum and Tarek Amara
TRIPOLI/TUNIS, April 21 (Reuters) - A Tunisian diplomat kidnapped in Libya pleaded with his government to negotiate with his Islamist captors, according to a video released by an Islamist group on Sunday evening.
Libyan Islamists have seized two Tunisian diplomats in the past month to demand the release of fellow militants jailed in Tunisia for attacking security forces there in 2011, according to the Tunisian government.
Entitled "message of the kidnapped Tunisian diplomat Mohammed Bel Sheikh to the Tunisian government and his family" the video, published on social media, showed the diplomat crying.
"Mr President, negotiate seriously with them. I want to return to my country Tunisia," the diplomat, who was sporting a beard, said. "They can kill me anytime."
"Mr President, I have three young children," he said. "Are you a father, Mr President?"
Bel Sheikh was kidnapped a month ago, while another Tunisian diplomat was snatched in the Libyan capital last week, the latest in a series of kidnappings of diplomats in the North African country.
At the end of the video, an Islamist group called Shabab al-Tawhid (Youth of Monotheism) added a message to the Tunisian government: "As you imprison ours we will imprison yours. As you kills ours we will kill yours."
Neither Libyan nor Tunisian officials were immediately available for comment but the diplomat's family confirmed it was Bel Sheikh who appeared in the five-minute video.
"The person who appeared in the video is my brother, that is sure ... we're suffering," his sister Samira bel Sheikh told Reuters.
"Where are the Tunisian authorities a month after his kidnapping. We haven't seen any action or negotiations," she said, adding that her brother had missed the birth of his youngest daughter. "Where is the president and the prime minister ?"
Libyan authorities are struggling to contain former rebels and Islamist militants who fought to depose ex-leader Muammar Gaddafi in 2011 and who have formed increasingly powerful and violent militias.
Last Tuesday, gunmen kidnapped Jordan's ambassador to Libya, demanding an Islamist militant be released from a Jordanian jail in exchange for the diplomat's freedom.
Foreign powers worry that Libya's porous borders and the absence of a functioning government are making the country a safe haven and transit point for militant Islamists heading for Syria, Egypt or sub-Saharan African countries.
Last week the interim prime minister resigned after just a month into the job, saying gunmen had tried to attack his family.
Tribal groups, militias and even local citizens are also resorting to road blockades as a negotiating tactic. Some rebel groups have also shut down the OPEC member's oil facilities, raising supply concerns on global oil markets. (Reporting by Feras Bosalum and Tarek Amara; Writing by Ulf Laessing; Editing by Susan Fenton)