TRIPOLI, Libya - A huge explosion rocked the headquarters of Libya's state oil company on Monday, after several gunmen stormed the building in the country's capital Tripoli.

Libya's UN-backed government said that several armed men stormed the offices of the National Oil Corporation (NOC) on Monday, and opened fire on staff and security guards.

As the masked gunmen engaged security guards in a deadly gun battle, a large explosion rocked the building in central Tripoli.

Some witnesses later told the local media that the explosion was caused by a suicide bomber who detonated himself while the other attackers continued to fire at security forces.

The explosion is said to have sparked a fire that spread through the entire office block. 

The head of the Libyan National Oil Company, Mustafa  Sanallah, said in a statement, "The building was heavily damaged due to the fire. Smoke is everywhere. The gunmen attacked the lower floors with random shooting and explosions. It’s a very violent attack.”

Sanallah added that a number of people had been killed.

As smoke engulfed the NOC building following the explosion, security forces allied to the Tripoli-based government arrived there and focussed on rescuing the staff, before putting an end to the attack.

Witnesses and the local media noted that security forces smashed windows and helped the staff escape the burning building.

Then, the government forces, along with security guards managed to kill two of the attackers, putting an end to the attack and regaining control of the building. 

Later, the Libyan Health Ministry confirmed that two people - both NOC employees - were killed in the attack and ten others were injured.

The media office of the Department of the Injured Affairs of the Health Ministry in Tripoli said that those injured were either directly hit in the exchange of fire or had inhaled too much smoke causing them to suffocate in the building.

Further confirming the death toll, Ahmad Ben Salim, a spokesperson for one of the most powerful factions in Tripoli - the Special Deterrence Force (SDF) said, “The death toll so far is two killed from NOC staff and two attackers."

The SDF and other security forces confirmed that one of the attackers had been gunned down. 

Later, reports noted that two of the attackers had been killed by security forces. 

Salim added, “We ringed the NOC building and together with other security forces we made sure the surrounding and inside of the NOC building was clear.”

Later, in a post on Facebook, the SDF said that they found body parts of the suicide bombers and they were “of black complexion.”

The group added that the building had been evacuated and that investigations were underway.

Meanwhile, after security forces regained control of the building, the National Safety Department evacuated employees from top floors of the building using firefighting equipment.

Later, speaking to the local media, some witnesses said that not one, but a series of explosions were heard during the attack.

Witnesses also pointed out that several people that were trying to escape the building were hurt by shattered glass after security forces smashed windows to help rescue them.

ISIS suspected

So far, no group has claimed responsibility for Monday’s attack but officials in the country suspected that the attack was orchestrated by the Islamic State militant group (ISIS).

However, Libya's Interior Ministry said in an official statement that initial indications showed the gunmen belonged to ISIS.

The terrorist organization has previously carried out attacks in Tripoli and other Libyan towns and cities.

In May this year, ISIS suicide bombers struck the headquarters of Libya's National Election Commission, killed 14 people.

The attack comes a week after Ghassan Salamé, head of the United Nations Support Mission in Libya (UNSMIL) warned the UN that ISIS is staging a comeback in Libya.

Informing the UN Security Council about the situation in Libya, Salame said, "ISIS presence and operations in Libya are only spreading. I alert this Council of the possibility that Libya may become a shelter for terrorist groups of all persuasions and ask the Council to help address with this looming threat."

He further claimed that a "facade of calm" existed in the capital, adding that Tripoli "stood on brink of all-out war." 

Meanwhile, Monday's attack also came merely three days after the North African country witnessed deadly clashes between rival armed groups that left at least 63 people dead in Tripoli.

Amid escalating violence, a fragile UN-backed ceasefire took hold. 

NOC head Sanallah, who is one of the country’s most influential non-political figures and has been credited with trying to root out corruption and increase Libyan oil production pointed out, “This incident serves to demonstrate the fragile security situation in our country and the need for additional measures to ensure NOC is able to withstand those that seek to halt Libya’s recovery."

He also added, "Far more important than the considerable damage to our building is the human cost of such an attack. Our people are our most precious asset."

Oil remains critical to Libya's economy and currently accounts for over 82 percent of its export earnings. 

The attack on NOC - which provides the vast bulk of Libya’s state income - was another attempt at targetting Libya's oil sector that has been repeatedly disrupted by violence since the country's late dictator Muammar Gaddafi was toppled in 2011 by a NATO-backed rebellion.