In a televised speech, Sayyed Hassan Nasrallah has called Tuesday's explosion "an exceptional event" that required unity and calm.
Hezbollah's leader has denied accusations that his Iran-backed movement has arms warehoused at Beirut port, calling for an investigation into the biggest explosion to hit the Lebanese capital.
In a televised speech on Friday, Sayyed Hassan Nasrallah called Tuesday's explosion "an exceptional event" that required unity and calm. The heavily armed Shia Hezbollah would make its political position clear after the dust settles, he added.
Nasrallah praised solidarity and aid pouring in from around the world, including a visit by French President Emmanuel Macron.
He said this presented an opportunity for Lebanon, already deep in financial crisis.
President Michel Aoun said the investigation would examine whether the cause was negligence, an accident or outside interference such as a bomb. Officials have said the explosive material was stored unsafely for years at the port.
'Negligence and corruption'
Nasrallah - whose faction is a big backer of the current government along with Aoun and other allies - asked why the ammonium nitrate was at the port no matter the cause of the blast.
"Even if a plane struck, or if it was an intentional act, if it turns out this nitrate had been at the port for years in this way, it means part of the case is absolutely negligence and corruption," he said.
Israel, which has fought many wars with Hezbollah and is an enemy state of Lebanon, has denied any role in the explosion.
Nasrallah called for a fair investigation to reveal the truth and strict accountability for anyone responsible without any political cover. Otherwise, "that means there is no state."
UN also calls for an investigation
The UN human rights office has called for an independent investigation into the Beirut explosion, insisting that “victims’ calls for accountability must be heard”.
Spokesman Rupert Colville of the UN High Commissioner for Human Rights cited the need for the international community to “step up” to help Lebanon with both a quick response and sustained engagement.
He said Lebanon is facing the "triple tragedy of a socio-economic crisis, Covid-19 and the ammonium nitrate explosion" that devastated the capital.
Colville also called for the poor and most vulnerable to be respected as Beirut and Lebanon rebuild, and urged Lebanese leaders to “overcome political stalemates and address the grievances of the population.” That was an allusion to large protests that broke out in Lebanon in October.
READ MORE: What’s behind Lebanon's economic crisis?
The death toll from the explosion has risen to 154, state news agency NNA cited Lebanon's health minister as saying on Friday.
Minister Hamad Hasan said one in five of the some 5,000 people injured in Tuesday's blast had required hospitalisation, and 120 were in critical condition, NNA reported.
WHO appeals for $15 million
The World Health Organization (WHO) is appealing for $15 million to cover emergency health needs in Lebanon.
The blast also destroyed 17 containers holding WHO medical supplies including personal protective equipment, the agency's regional office for the Middle East said in a statement late on Thursday.
Five hospitals in the area affected by Tuesday's blast are either not functioning or partially functioning, and early reports indicate that many health centres and primary care facilities are also damaged or out of action, it said.
Three hospitals in #Beirut are non-functional & 2 others are partially damaged & functioning well below capacity, resulting in a loss of 500 hospital bed capacity. Many health centers & primary care facilities are also damaged and/or out of action as a result of the blast. pic.twitter.com/FO3lyYkJcH— WHO EMRO (@WHOEMRO) August 6, 2020
Rescuers recover more bodies
Rescue teams are searching the rubble of Beirut’s port for bodies, nearly three days after the massive explosion.
French and Russian rescue teams with dogs are searching the area, and at least three more bodies were recovered during the past 24 hours.
The government has launched an investigation as it faces mounting criticism, with many Lebanese blaming the catastrophe on negligence and corruption.
The blast was apparently caused by the ignition of 2,750 tonnes of ammonium nitrate, a chemical used for explosives and fertiliser, that had been stored at the port since being confiscated from an impounded cargo ship in 2013.
The blast shredded a large grain silo, devastated neighbourhoods near the port and left several city blocks littered with glass and rubble.
The UN children's agency UNICEF has said nearly 80,000 children are among the 300, 000 people left homeless, including many who have been separated from their families.