The US Secretary of State has said that a move by Israel's parliament towards annexation of the occupied West Bank would threaten Washington's plan to end the conflict in Gaza.

"That's not something we can be supportive of right now," Marco Rubio said before leaving for Israel as part of US efforts to shore up a fragile ceasefire deal.

In an apparent attempt to embarrass Israel's Prime Minister Benjamin Netanyahu, far-right politicians took the symbolic step of giving preliminary approval to a bill granting Israel authority to annex the West Bank.

The Palestinians claim the West Bank - occupied by Israel since 1967 - as part of a hoped-for independent state.

Last year, the International Court of Justice - the UN's top court - said Israel's occupation was illegal.

Netanyahu has previously spoken in support of annexing West Bank land but has not advanced this due to the risk of alienating the US - Israel's most important ally - and Arab countries which have built relations with Israel after decades of enmity. 

Ultra-nationalists in Netanyahu's governing coalition have repeatedly called for Israel to annex the West Bank outright, though the bill was put forward by MPs outside the government.

The bill passed in a 25-24 vote. It is unclear whether it has support to win a majority in the 120-seat Knesset (parliament), and there are ways the prime minister can delay or defeat it.

The Palestinian foreign ministry condemned the Knesset's move, saying Israel would have no sovereignty over Palestinian land.

Israel has built about 160 settlements housing 700,000 Jews during its occupation of the West Bank and East Jerusalem. An estimated 3.3 million Palestinians live alongside them.

The settlements are illegal under international law - a position supported by an advisory opinion of the International Court of Justice last year.

As he boarded the plane to Israel, Rubio said annexation would be "counterproductive" and "threatening" for the peace deal - reiterating US opposition to annexation.

His visit on Thursday comes hot on the heels of trips by US Vice-President JD Vance and two special envoys, as the Trump administration attempts to push for the start of talks on the second critical phase of his 20-point Gaza peace plan.

The first phase - which includes a ceasefire, the partial withdrawal of Israeli forces and an influx of aid - came into effect earlier this month.

Both Israel and Hamas have accused each other of breaching the agreement over deadly incidents, but it has so far held.

Rubio voiced similar optimism to that of Vance for preserving the ceasefire.

"Every day there'll be threats to it, but I actually think we're ahead of schedule in terms of bringing it together, and the fact that we made it through this weekend is a good sign," he said.

The second phase of the peace plan would involve setting up an interim government in Gaza, deploying an international stabilisation force, the withdrawal of Israeli troops, and the disarmament of Hamas.

The war in Gaza began with the Hamas-led attack on southern Israel on 7 October 2023, in which around 1,200 people were killed and 251 taken hostage.

In the ensuing conflict, more than 68,000 Palestinians have been killed in Gaza, according to the territory's Hamas-run health ministry, whose figures are seen by the UN as reliable.