Twin car bomb blasts killed two people in the Libyan capital at dawn on Sunday on the first day of the Muslim Eid al-Fitr holiday and officials blamed loyalists of now slain dictator Muammar Gaddafi.
Tripoli's security chief Colonel Mahmud al-Sherif told AFP the bombs were detonated by remote control and struck near a military academy and the interior ministry.
"They were two car bombs detonated by remote control," Sherif said, adding that four people were also wounded in the first blast.
The attacks struck on the first day of the Eid al-Fitr festival that ends the Muslim fasting month of Ramadan.
The first car bomb blew up at 6:00am (0400 GMT) near a military academy on Omar al-Mokhtar Avenue -- a main Tripoli thoroughfare that was closed briefly to traffic -- and the second near the interior ministry.
An AFP correspondent said checkpoints were set up on other major streets in the city centre.
When the avenue was later reopened to traffic, the only sign of the blast was some broken glass on the scorched pavement. Remains of the vehicle had been removed.
The second bomb was concealed in a taxi and blew up in a sidestreet near the interior ministry. There were no casualties.
Earlier this month, three men suspected of preparing bomb attacks were killed during a police raid near Tripoli but several of them managed to flee, authorities said.
According to Sherif, Sunday's attacks were orchestrated by "the same sleeper cell," because the explosives and methods used were the same as in an attack in central Tripoli on August 3 that wounded one person.
"This groups is funded by members of the old regime who are in Tunisia and Algeria," he added.
Dozens of officials and relatives of Gaddafi fled to neighbouring Tunisia and Algeria and other countries after the overthrow of his regime.
Authorities have accused them of seeking to destabilise post-revolution Libya, where earlier this month the country's newly-elected national assembly held its first session.
Deputy interior minister Omar al-Kadhrawi told AFP that security services had been tipped off on the possibility of attacks.
"For the past three days, we had information that such attacks could take place, but it is difficult to control everything because the country is awash with weapons," he said.
Authorities are hunting for more car bombs, he said.
Asked if security would be reinforced, he added: "We are doing our best. We cannot do more than that.
"I can reassure you. They (Gaddafi loyalists) are cowards.
"Rigging a car with explosives is the most they can do," he told hundreds of Muslims who gathered in Tripoli's central Martyrs' Square for the traditional early morning Eid al-Fitr prayers in spite of the bombings.
Most of the urban violence to have hit Libya in the wake of last year's revolt which ousted Gaddafi has taken place in the eastern city of Benghazi.
Earlier this month. gunmen shot dead a high-ranking defence ministry official in the city -- Libya's second largest -- one of his sons told AFP. A bomb blast also shook the military intelligence building in Benghazi, which was the cradle of the uprising.