By Issam Abdallah and Ellen Francis
BEIRUT (Reuters) - A top U.S. diplomat said on Thursday the FBI would join a probe of the massive Beirut explosion that killed at least 172 people, urging change in Lebanon to "make sure something like this never happens again".
On a tour of a demolished Beirut neighbourhood, U.S. Undersecretary for Political Affairs David Hale said Lebanon needed "economic and fiscal reforms, an end to dysfunctional governance and to empty promises".
The explosion at Beirut port injured 6,000 people and forced around 300,000 out of their homes in the city, which was already sinking deep into financial crisis. Some 30-40 people remain missing.
Authorities have blamed the Aug. 4 blast on a huge stockpile of ammonium nitrate stored for years at the port without safety measures.
"The FBI will soon join Lebanese and international investigators at the invitation of the Lebanese to help answer questions about the circumstances that led up to this explosion," Hale said on Thursday.
Lebanese President Michel Aoun has said the investigation will look into whether the cause was negligence, an accident or possibly "external interference".
Aoun has asked France for satellite imagery for the probe. A UK Royal Navy vessel was also deployed to Beirut to survey the site.
An Israeli seismological expert said on Thursday the explosion was preceded by a series of blasts, the last of which was combustion of fireworks.
Authorities have estimated losses from the blast at $15 billion, a bill Lebanon cannot pay: it already defaulted on its enormous sovereign debt in March and IMF talks had stalled.
Humanitarian aid has poured in. But foreign countries that once helped have made clear they will not give funds to help Lebanon out of economic collapse without reforms to tackle state corruption and waste.
Hale, the No. 3 U.S. diplomat, said Washington would back any new government that "reflects the will of the people" and enacts reforms. The fallout from the explosion forced the cabinet to resign this week.
But agreement on a new one could be daunting in a country with factional rifts and a sectarian power-sharing system. Public anger has grown at a political elite in power for decades, which many blame for the country's woes.
The now-caretaker government came to office in January with backing from various political parties, including the heavily armed Shi'ite Muslim Hezbollah. Together with its allies, they have a majority of seats in parliament.
The United States classifies Hezbollah, which is backed by Tehran, as terrorist. Iran's Foreign Minister Mohammad Javad Zarif landed in Beirut on Thursday evening, local media said.
Security forces were heavily deployed in Beirut on Thursday, stopping protesters from reaching a legislative session.
"They are all criminals, they are the ones who caused this catastrophe, this explosion," said protester Lina Boubess, 60.
"Isn't it enough that they stole our money, our lives, our dreams and the dreams of our children? What more do we have to lose?"
Parliament approved an earlier government decision declaring a state of emergency, which activists criticized as an attempt to suppress dissent. It also confirmed the resignations of eight MPs who quit after the blast.
(Reporting by Tom Perry, Issam Abdallah, Ellen Francis and Maher Chmaytelli; Writing by Ellen Francis; Editing by William Maclean, Mark Heinrich, Dan Grebler and Giles Elgood)