BEIRUT: As Lebanon Friday mourned more than 46 people killed in ISIS-claimed twin suicide bombings in a southern Beirut suburb, security and judicial officials focused their probe on determining the identities of the two bombers and how they managed to enter the densely populated area during rush hour. Meanwhile, top Lebanese leaders called for national unity to thwart ISIS’ plans to incite sectarian strife through its deadliest attack deep into the southern Beirut suburb of Burj al-Barajneh Thursday.

In its statement claiming responsibility for the blasts that killed at least 46 people and wounded over 200, ISIS did not reveal the names of the two suicide bombers.

“Investigation is concentrating now on how the terrorists entered the area, and who helped them in the attack and who provided them with the explosives,” a judicial source told The Daily Star.

“The big number of casualties shows that the terrorists had previously inspected the area well, choosing a very narrow street known for its dense population,” the source said.

“They [terrorists] waited for the rush hour to blow themselves up in order to cause the biggest number of dead and wounded, in addition to heavy material damage and the state of panic caused by this terrorist act,” he added.

A security source told The Daily Star that the security plan enforced in Beirut’s southern suburbs more than a year and a half ago had prevented many bomb-rigged vehicles from entering the area as a result of checkpoints manned by the Army and General Security personnel who searched incoming vehicles and motorbikes.

However, the plan did not take into account the possibility of terrorists entering the area on foot to carry out such attacks, the source said.

“If we ascertain that the terrorists entered the suburbs on foot, then this means that we have entered a new and very dangerous stage,” the source said. He added that any new security measures that would involve searching pedestrians and checking their identity cards would be “extremely difficult and complicated.”

Military Prosecutor Saqr Saqr and State Prosecutor Samir Hammoud, who visited the bombing site Friday, confirmed that only two suicide bombers blew themselves up in the attack, disputing reports of a third bomber.

“A suicide attacker on a motorbike blew himself up using 7 kilograms of explosives, which caused mass destruction in the area and extensive damage. The second suicide bomber was wearing an explosive belt weighing 2 kilograms,” Hammoud said in Burj al-Barajneh.

He said that security forces are inspecting surveillance cameras in the area, confirming “the attack was conducted by two suicide bombers.”

“Another explosive belt was found at the scene and it will be compared with the belt confiscated from a suspect detained Thursday in the northern city of Tripoli,” he added.

Police Thursday arrested a suspect identified as Ibrahim J. in the Qibbeh neighborhood of Tripoli who was found wearing an explosive belt hours before the attack in Beirut. Saqr said security forces are cooperating in the investigation to check rumors about a third suicide bomber.

“The alertness of security forces saved Lebanon from another bombing in the north,” Saqr said, referring to the suspect who was detained by the Internal Security Forces in Qibbeh.

The Army Thursday said the attack was carried out by two suicide bombers, and that the body of a third who failed to detonate his explosive device was found at the scene of the second blast.

A day after the bombings, Prime Minister Tammam Salam ordered the Army and police chiefs to beef up measures across the country in order to consolidate security and stability.

“The barbaric crime in Burj al-Barajneh didn’t target a certain area or sect, but marked Lebanon with blood,” Salam said during a special meeting with the Army and police chiefs and senior military and security officials at the Grand Serail. The meeting was also attended by the defense, interior, justice and finance ministers.

Salam also tasked the Higher Relief Committee with surveying the blast site to compensate those who were affected by the attack.

Meanwhile, Speaker Nabih Berri and Salam called for national unity to foil ISIS attempts to stir up sectarian strife in Lebanon.

Speaking during a legislative session in Parliament to endorse urgent draft laws, Berri urged the Arab League, the U.N. Security Council, Islamic organizations and the Vienna meeting on Syria to declare “a global war” on takfiri groups.

“Lebanon is facing a new terrorist war on its sovereign borders, where the Zionist aggressiveness and takfiri terrorism meet together to undermine its stability,” he said.

Berri said Lebanon’s eastern border, Tripoli, Beirut and its mountains are threatened with similar bombings “if we don’t act to face bases of terrorism.”

“The Lebanese people and their vibrant forces are called upon to show the power of their national unity and understanding on their military and security forces and reactivating their governmental departments,” Berri said.

“We call on the Lebanese to be fully vigilant and wary of killings and strife schemes by defeated terrorist groups which are seeking suicide by undermining Lebanon’s stability,” he added.

Berri also said that top Hamas leaders have assured him that the suicide bombers did not come from the Burj al-Barajneh refugee camp.

“Khaled Meshaal and Ismail Haniyeh confirmed to me that the Burj al-Barajneh bombers, said to be Palestinian, were not from the refugee camp,” Berri said.

Addressing the Parliament session, Salam said national unity was the only way to shield the country against threats. “We have to work together to face these strife dimensions. Strife is more severe than killing,” he said.

Hezbollah leader Sayyed Hasan Nasrallah is expected to speak on the Burj al-Barajneh attack in a televised speech at 8:30 p.m. Saturday.