The head of Lebanon's Shiite movement Hezbollah warned Saturday that a long-delayed US peace plan could see Palestinian refugees permanently settled in host countries across the region.

Speaking days after the US announced a May conference in Bahrain to lay out economic aspects of its long-awaited Israeli-Palestinian peace plan, Hezbollah chief Hassan Nasrallah warned of an "ominous deal aimed at eliminating the Palestinian cause".

He said the conference's focus on economic issues "may open the door wide open to the question of naturalising the Palestinian brothers in Lebanon and the countries where they are located".

The right of return for more than 700,000 refugees who were expelled or fled during the creation of the State of Israel in the late 1940s -- and their millions of descendants -- is a key pillar of the Palestinian cause.

The vast majority cling tightly to hopes, enshrined in a key UN Security Council resolution, of returning to lands their families once owned but which are now inside Israel.

An estimated 174,000 Palestinian refugees live in Lebanon, according to a census by national authorities in 2017.

The UN estimates there are tens of thousands more.

Lebanon's Palestinian camps suffer poverty, overcrowding, unemployment, poor and dangerous housing conditions and a lack of infrastructure.

Today, "it's not enough to say we're all against naturalisation -- the danger of naturalisation is approaching," Nasrallah said during a televised address marking the 19th anniversary of Israel's withdrawal from southern Lebanon.

He called for an urgent meeting between government and Palestinian officials in Lebanon to "develop a plan to confront the danger".

The Palestinian leadership has said it will boycott the June 25-26 meeting in Manama, where the declared aim is to promote Palestinian prosperity as part of Trump's "deal of the century".

The Trump administration is expected to unveil its long-awaited plan possibly as early as next month.

The Bahrain conference could see large-scale investment pledges for the Palestinian territories but is unlikely to focus heavily on the political issues at the core of the conflict, such as the question of Palestinian refugees.