Britain's Prime Minister Keir Starmer. AFP
A growing number of longtime Israeli allies have shifted positions in recent months as Israel has intensified its war on Gaza.
The besieged Palestinian territory has suffered vast destruction, death and lack of food that have resulted in a major humanitarian crisis.
World leaders will gather for a key debate at the UN General Assembly in New York this week, where the two-state solution to the Israeli-Palestinian conflict will be front and centre.
Around 10 nations are expected to recognise a Palestinian state in the coming days, with UK media outlets like the BBC, reporting that Prime Minister Keir Starmer would announce the policy shift on Sunday -- over fierce Israeli objection.
Starmer had said in July that Britain would formally recognise the State of Palestine if Israel did not take "substantive steps" towards a ceasefire with Hamas by the time the UN General Assembly convened.
The Labour leader said at the time that the move would make "a contribution to a proper peace process, at the moment of maximum impact for the two-state solution".
Portugal's foreign ministry said on Friday that it would also formally declare its recognition on Sunday.
Lisbon had already announced in July that it intended to do so, citing the "extremely worrying evolution of the conflict" as well as the humanitarian crisis and Israel's repeated threats to annex Palestinian land.
Since then, Israel has bombarded Gaza, a UN-backed hunger monitor has declared a famine in part of the territory, and the Israeli military has said it will use "unprecedented force" to capture Gaza City.
France and Canada are among the other Western nations planning to recognise a Palestinian state at the UN gathering in the coming week.
Israel has vehemently opposed the moves and has reportedly threatened to annex the West Bank in response.
UN Secretary-General Antonio Guterres told AFP on Friday that the world "should not feel intimidated by the risk of retaliation" from Israel.
Israel's war on Gaza has killed at least 65,208 Palestinians, mostly women and children, according to figures from the Palestinian health ministry that the United Nations considers reliable.
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