The Islamic State group has claimed a deadly suicide bombing at a checkpoint in Libya's oil heartland, as EU foreign affairs chief Federica Mogherini seeks to shore up support for a unity government.
Fears that the jihadists are establishing a new stronghold on Europe's doorstep have added urgency to efforts to bring together warring factions in a country beset by years of turmoil.
IS's Libya branch released a statement saying that Thursday's attack in Ras Lanouf, east of its coastal bastion of Sirte, was carried out by a foreign fighter using an explosives-packed car.
Six people, including a baby, were killed, according to Libya's Red Crescent.
Another suicide bomber on Thursday attacked a police training school in Zliten, west of Tripoli, killing more than 50 people, a security source said.
No group has yet claimed responsibility for that blast, which left buildings charred and turned cars into twisted black wrecks.
It was the deadliest attack since the 2011 revolution that toppled longtime dictator Moamer Kadhafi.
- 'Unity best way' -
UN Secretary-General Ban Ki-moon urged Libya's rival parliaments to throw their support behind a disputed national unity government deal.
"These criminal acts serve as a strong reminder of the urgency to implement the Libyan political agreement and form a government of national accord," he said, referring to the suicide bombings.
"Unity is the best way for Libyans to confront terrorism in all its forms."
Mogherini was due to hold talks in Tunis on Friday with Libyan politicians including Fayez al-Sarraj, who was named in the UN-brokered national unity deal as prime minister designate.
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The agreement was signed last month by a minority of lawmakers but has yet to win the full support of the two legislatures.
The heads of the parliaments have warned that the deal has no legitimacy and that the politicians signing the agreement represented only themselves.
On Thursday Mogherini urged Libyans to back the unity deal.
"The people of Libya deserve peace and security and... they have a great opportunity to set aside their divisions and work together, united, against the terrorist threat facing their country," she said.
A unity government "will also help preserve Libya's resources, defeat terrorists that want to undermine Libya's prosperity, and restore stability and security throughout the country," she added.
IS has been expanding its foothold in Libya, exploiting the instability that has gripped the country since the 2011 uprising.
The turmoil has also led to Libya's rise as a stepping stone for migrants crossing the Mediterranean to Europe.
On Monday IS launched an offensive against the oil terminals in Ras Lanouf and nearby Al-Sidra, after trying for weeks to push east from Sirte.
The terminals are located in the so-called "oil crescent" along the northern coast, and officials have warned that the already crumbling Libyan state could be paralysed if the jihadists seize control of oil resources.
Libya has had rival parliaments and administrations since August 2014, when an Islamist-backed militia alliance overran Tripoli, forcing the government to take refuge in the east.
Calls have been growing for a possible foreign military intervention to bring stability and contain IS, which is reported to have at least 3,000 fighters in Libya.
In a report to the UN Security Council in November, International Criminal Court chief prosecutor Fatou Bensouda said that IS was responsible for at least 27 car and suicide bombings in Libya in 2015.
The group claimed responsibility for suicide car bombings in the eastern town of Al-Qoba in February that killed at least 40 people.