Lebanese army bulldozers plowed through wreckage to reopen roads around Beirut's demolished port Thursday, a day after the government pledged to investigate this week's devastating explosion and placed port officials under house arrest.

The blast Tuesday, which appeared to have been caused by an accidental fire that ignited a stockpile of ammonium nitrate at the port, rippled across the Lebanese capital, killing at least 135 people, injuring more than 5,000 and causing widespread destruction.

French President Emmanuel Macron was expected to visit later Thursday amid pledges of international aid. But Lebanon, which was already mired in a severe economic crisis, faces a daunting challenge in rebuilding. It's unclear how much support the international community will offer the notoriously corrupt and dysfunctional government.

The tiny Mediterranean country was already on the brink of collapse, with soaring unemployment and a financial crisis that has wiped out people's life savings. Hospitals were already strained by the coronavirus pandemic, and one was so badly damaged by the blast it had to treat patients in a nearby field.

Anger is mounting against the political class that has dominated the country since the 1975-1990 civil war, which has long been seen as hopelessly corrupt and incapable of providing even basic services like electricity and trash collection.

The investigation is focusing on how 2,750 tons of ammonium nitrate, a highly explosive chemical used in fertilizers, came to be stored at the facility for six years, and why nothing was done about it.

The Port of Beirut and customs office are notorious for being among the most corrupt and lucrative institutions in Lebanon, where various factions and politicians, including the Iran-backed Hezbollah militant group, hold sway.

Fueling speculation that negligence was to blame for the accident, an official letter circulating online showed the head of the customs department had warned repeatedly over the years that the stockpile of ammonium nitrate was a danger and had asked judicial officials for a ruling on a way to remove it.

Authorities have cordoned off the port itself, where the blast left a crater 200 meters (yards) across and shredded a large grain silo, emptying its contents into the rubble. Estimates suggested about 85% of the country’s grain was stored there.

Lebanon is highly dependent on imports, and the destruction of the port, along with the worsening cash crisis, have raised fears of shortages.

Two planeloads of French rescue workers and aid were sent to Beirut, and Macron was to arrive Thursday to offer support for the former protectorate. The countries retain close political and economic ties.

Other countries, including Greece, Qatar, Kuwait, Turkey and the European Union, have dispatched medical supplies, humanitarian aid and search-and-rescue teams.