ABU DHABI, United Arab Emirates (CNN) -- A tense calm prevailed over Libya's capital Thursday after days of chaos left at least seven people dead -- including a 12-year-old boy.

But it's unclear if the violence is really over -- or even who the warring groups are.

Sounds of heavy gunfire and explosions echoed across Tripoli on Wednesday night, sending waves of confusion and panic as residents weren't sure who was behind the attacks.

Medical sources in Abu Saleem Hospital said two people, including a 12-year-old boy, died Wednesday from injuries sustained in the clashes, the state news agency LANA reported. The hospital also said it was treating a number of injured from the violence.

LANA said it was not clear what groups were involved in Wednesday's fighting. It quoted witnesses as saying the densely populated Abu Saleem area was in a state of "panic and fear" as fighting closed off main roads in the area, including the one leading to the international airport.

It was not clear if the fighting Wednesday was linked to deadly clashes in another southern Tripoli neighborhood a day earlier.

Attack at oil protection force

On Tuesday, an armed group attacked the headquarters of the Petroleum Facilities Protection Guard (PFG) in the Salaheddin district of the capital.

The Libyan government said at least five people were killed and nearly two dozen others wounded in the heavy fighting.

The PFG -- a Ministry of Defense force tasked with protecting Libya's oil field -- said an armed group from the western city of Zintan surrounded at attacked its Tripoli headquarters.

It said the group had previously been tasked with securing Al-Sharara field -- one of Libya's biggest oil fields in the south of the country.

The attackers used light and heavy weapons, including anti-aircraft weapons, and injured at least six people, PFG said in a statement.

The armed group fled the scene after back up forces arrived, the statement said.

Tripoli's Supreme Security Committee (SSC), a security body in the capital, said its forces who were protecting the PFG headquarters came under fire by the attackers. A commander of one of its brigades was killed in the attack, the SSC said in a statement.

The security body also said the armed group fled to a nearby former military base and positioned snipers on the rooftops of the buildings. Clashes between members of the SSC and the armed group ensued.

Dozens of casualties were reported by the SSC. It said one of its members was killed in addition to three Ministry of Defense personnel in the clashes.

The SSC said Tuesday's violence was related to Wednesday's clashes, but it was unclear exactly how.

A sign of the times

While inter-militia clashes in the Libyan capital became less frequent over the past year, the latest fighting underscores one of the biggest challenges facing Libya.

Since the 2011 fall of Moammar Gadhafi's regime, the country has been awash in weapons and militias. Some of these militias have been legitimatized by the Libyan government, while others have not.

As militias refuse to disarm or work under the authority of the state, Libya is still struggling to build its security forces -- something the prime minister said would take years.

The government heavily relies on militias that are mostly divided along regional lines to try to secure the country.

More attacks elsewhere

In addition to Tripoli's violence, three car bombs exploded Wednesday evening across the southern city of Sabha, killing at least two people and injuring 17 others, LANA reported.

One of the car bombs exploded on a commercial street, a second blew up near a security directorate and the third went off outside a hotel in the center of town, the agency said.

CNN's Holly Yan contributed to this report.