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By Tarek Amara
TUNIS, April 18 (Reuters) - Libyan militants who kidnapped a Tunisian diplomat in Tripoli on Thursday have demanded the release of Islamist fighters detained in Tunisia, its foreign minister said.
Such kidnappings have become commonplace as Libya's political landscape fragments, and Mongi Hamdi also said Tunisia was considering reducing its diplomatic mission in the country.
The Tunisian embassy adviser taken on Thursday became the second Tunisian diplomat to be kidnapped in the Libyan capital within a month.
"We will try to interact with the kidnappers to secure the lives of our diplomats," Hamdi told reporters on Friday, without elaborating.
On 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.
Egypt moved most of its diplomatic staff out of Libya in January after militant group kidnapped several diplomats to secure the release of one of their leaders in Egypt.
Foreign powers worry that the country's porous borders and absence of a functioning government are making it a safe haven and transit point for militant Islamists heading for Syria, Egypt or sub-Saharan countries.
Libyan authorities have been unable to disarm 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 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 also resort to road blockades as a negotiating tactic. Some have resorted to shutting down the OPEC member's oil facilities.
Hamdi said the kidnappers of the Tunisian diplomatic advisor belonged to "the family of a group of terrorists detained in Tunisia because of their involvement in attacks (three years ago) against security forces in Rouhia city."
Two soldiers and two militants were killed during fighting in the northeastern Tunisian city in May 2011, the first clashes between Islamists and security forces since Tunisia's Arab spring revolution three years ago. Police arrested several Algerian and Libyan gunmen.
(Reporting by Tarek Amara; Editing by Ulf Laessing and John Stonestreet)