Trump calls Hezbollah a menace 'to the whole region' after meeting Lebanese PM

US President Donald Trump assailed Hezbollah and expressed support for Lebanon in its fight against the Islamic State (IS) group, in a joint news conference with Lebanese Prime Minister Saad Hariri at the White House on Tuesday.

"Hezbollah is a menace to the Lebanese state, the Lebanese people and the entire region," Trump said.

"The group continues to increase its military arsenal, which threatens to start yet another conflict with Israel... With the support of Iran, the organisation is also fuelling humanitarian catastrophe in Syria."

Hezbollah, which is designated a terrorist organisation by the US State Department, is part of the Lebanese government and is currently leading a campaign against IS militants in the country’s east.

Asked how Washington can help Lebanon cope with the influx of Syrian refugees, Trump talked up advances by US-backed forces against IS in Syria.

The US president praised Lebanon's efforts to guard its borders to prevent IS and other militant groups from gaining a foothold inside their country, and promised continued American help.

He also praised the “resilience” of the Lebanese people in the “face of terror”.

"America's assistance can help ensure that the Lebanese army is the only defender Lebanon needs," Trump said.

Trump also criticised Syrian President Bashar al-Assad and slammed his predecessor Barack Obama for not enforcing the "red line" when the previous administration did not strike the Syrian government for suspected use of chemical weapons in 2013.

"I'm not a fan of Assad. I certainly think that what he's done to that country and to humanity is horrible," Trump said.

"I am not somebody that will stand by and let him get away with what he tried to do, and he did it a number of times."