Hundreds of Beirut residents fled their homes late on Sunday after Israel said it was preparing attacks on sites linked to the financial operations of Lebanon's Hezbollah group within hours and told people to leave those areas immediately.
Soon after the Israeli warning, several blasts were heard and a large fire was seen in Beirut's southern suburbs. There was no immediate information on what caused the explosion, or details of any casualties.
Panicked crowds clogged the streets and caused traffic jams in some parts of Beirut as they tried to get to neighbourhoods thought to be safer, witnesses said.
"Residents of Lebanon, the IDF (Israeli military) will begin attacking infrastructure belonging to the Hezbollah Al-Qard Al-Hassan Association - get away from it immediately," the military's spokesperson said in a statement on X.
Al-Qard al-Hassan - which the U.S. has said is used by Iran-backed Hezbollah to manage its finances - has more than 30 branches across Lebanon including 15 in densely populated parts of central Beirut and its suburbs.
There was no immediate statement from the organisation, Hezbollah or the Lebanese government.
Asked by journalists whether the branches could be considered military targets, a senior Israeli intelligence official said: "The purpose of this strike is to target the ability of Hezbollah economic function both during the war but also afterwards to rebuild and to rearm ...on the day after."
By Amina Ismail and Nidal al-Mughrabi