Lebanon's President Michel Aoun dismissed as "impossible" suggestions that Beirut's catastrophic explosion was caused by a blast from a deposit of Hezbollah arms, but said all possibilities would be investigated.

The Lebanese authorities are probing what caused the massive amount of ammonium nitrate warehoused unsafely at the port to detonate on August 4, killing 178 people, injuring 6,000 and destroying swathes of the city.

Aoun, whose Christian party the Future Patriotic Movement is an ally of the powerful Iran-backed Hezbollah movement, told Italian daily Corriere della Sera in an interview published on Tuesday that Hezbollah did not store weapons at the port, echoing comments by the group's leader earlier this month.

"Impossible, but serious events like these light up spirits and imagination," Aoun said when asked about people advancing the hypothesis but added that "even this lead will be investigated."

The Future Patriotic Movement signed a memorandum of understanding with Hezbollah in 2006, and Both parties are part of a larger coalition called the March 8 Alliance. The outgoing government led by Prime Minister Hassan Diab was nominated by the two parties and their allies in parliament. 

Hezbollah leader Sayyed Hassan Nasrallah has previously denied accusations that his heavily armed movement had weaponry warehoused at the Beirut port. He has said that the group would wait for results of the investigation but if it turns out to be an act of sabotage by Israel then it would "pay an equal price."

Hezbollah, which exercises sway over the government in Lebanon, has fought several wars with Israel and is classified by the United States as a terrorist group. The movement has never been shy about blaming Israel for any misfortune in Lebanon. 

Israel has offered aid to Beirut and has denied any involvement in the blast.

Aoun said the probe is looking into whether neglect, an accident or "external interference" caused the blast.

"Although it seems that [it] has been an accident, I want to avoid being accused of not having listened to every voice," Aoun told the Italian daily.

He noted that many people claimed seeing airplanes fly by the port just before the blast and said although "not very credible," they should be listened to.

Responding to calls for the president to resign over the massive blast, Aoun has said it is "impossible" for him to leave office, adding that his departure "would lead to a power vacuum." 

"If I were to resign, one would need to organize elections right away. But the current situation in the country does not allow the organization of such elections," Aoun said. 

(With input from agencies)