Kidnappers seized Egypt's cultural attache and three other embassy staff in the Libyan capital today a day after a group snatched another Egyptian official in the city.
In the south, meanwhile, the toll from ethnic clashes rose to 88 dead and more than 130 wounded, a further sign of the chronic instability that has plagued Libya since the 2011 uprising ousted Moamer Kadhafi.
The four diplomats were kidnapped early on Saturday morning, a Libyan foreign ministry spokesman said,
Said Lassoued told AFP that "the cultural attache and three other staff were kidnapped in Tripoli".
The abductions came a day after an unknown group seized an administrative adviser at Egypt's embassy, and despite Libya's announcement of "reinforced security measures" there.
Foreigners have been targeted several times in recent weeks: two Italians were seized last week in east Libya and a South Korean trade representative was released by security forces on Wednesday, three days after he was abducted in Tripoli.
Prime Minister "Ali Zeidan" was himself briefly abducted by a former rebel militia last October.
A Libyan security official would not rule out that the kidnapping of the Egyptian administrative official was a response to the arrest in Egypt on Friday of a prominent former rebel commander who fought in the uprising.
Shaaban Hadeia, head of the Operations Centre of Libya's Thuwar (revolutionaries), was arrested in Alexandria, the source added.
The Operations Centre had posted on Facebook that there could be a "possible reaction from the thuwars".
But one of the group's leaders, Adel al-Ghariani, told AFP the group was not involved in the kidnappings and called for Hadeia's release.
The presidency of the General National Congress, Libya's highest political authority, also ordered its mission in Cairo to demand an explanation for the ex-rebel leader's arrest and to seek his release.
Cairo has yet to confirm his detention.
Libya has struggled to integrate rebel groups that helped topple Kadhafi into the security forces. Some militias have carved out their own fiefdoms, each with its own ideology and regional allegiances.
The situation is also dire in eastern Libya, where radical Islamists have been accused of carrying out dozens of attacks on security forces and Western interests, mostly in second city Benghazi.
Two blasts hit Benghazi on Saturday without causing any casualties, one targeting a military intelligence base and the other a Koranic school.
Security forces said on Friday they had arrested four people who had a "list of officers who had already been assassinated and to assassinate" in an operation that left one soldier dead.
Authorities are also faced with sporadic unrest in the south, where the death toll from two weeks of ethnic clashes near the region's main city of Sebha rose to 88 dead on Saturday.
Abdallah Ouheida, director of Sebha hospital, told AFP that "between the outbreak of the fighting on January 11 and Friday evening, the number of dead totaled 88".
He said the full death toll was almost certainly higher as casualties had also been taken to other hospitals, adding that there had been sporadic clashes on Saturday but no new reports of casualties.
The fighting erupted between members of the Toubou minority, a non-Arab ethnic group, and armed Arab tribesmen of the Awled Sleiman.
There has since between fighting between the Awled Sleiman and other Arab tribes that is reported to have involved Kadhafi supporters.
Libya's General National Congress declared a state of emergency in the south on January 18 at an extraordinary session to discuss the violence in Sebha.