US President Joe Biden on Wednesday promised $100 million in additional aid for Lebanon as he pressed the crisis-wracked nation to undergo reforms.

"Today I'm announcing nearly a $100 million in new humanitarian assistance," Biden told a UN-backed donor conference for Lebanon led by France.

"But no amount of outside assistance will ever be enough if Lebanon's leaders do not commit to do the hard but necessary work of reforming the economy and combating corruption," he said.

"It's essential. It has to start now," Biden said. "There's no time to waste. You know it. We are there to help if you do it."

The Biden administration did not immediately specify where the new funding would go but Biden said it was in addition to $560 million in humanitarian assistance devoted to Lebanon over the past two years.

The Lebanon conference comes one year after an explosion at the Beirut port killed at least 214 people, the latest trauma for a nation with an economy in free-fall and without a stable government.

"I send my deepest condolences to all those who were injured and lost loved ones and all those still struggling to recover from this trauma," Biden said.

"We also recognize that the people of Lebanon have suffered more over the past year because of avoidable political and economic crisis."