Jeremy Corbyn has condemned the "illegal and inhumane" actions of Israeli troops following violence at the border with Gaza.
The Labour leader said the Israeli response, which has claimed the lives of at least nine Palestinians and wounded scores more, was an "outrage".
Israeli troops opened fire from across the border, killing at least nine Palestinians - including a journalist - and wounding 491 others on Friday in the second mass protest in eight days.
In a message read out at a demonstration outside Downing Street, Mr Corbyn said: "The killing and wounding of yet more unarmed Palestinian protesters yesterday by Israeli forces in Gaza is an outrage.
"The majority of the people of the Gaza Strip are stateless refugees, subject to a decade-long blockade and the denial of basic human and political rights.
"More than two thirds are reliant on humanitarian assistance, with limited access to the most basic amenities, such as water and electricity.
"They have a right to protest against their appalling conditions and the continuing blockade and occupation of Palestinian land, and in support of their right to return to their homes and their right to self-determination.
"Firing live ammunition into crowds of unarmed civilians is illegal and inhumane and cannot be tolerated.
"We stand in solidarity with the Israelis who have taken to the streets this last week to protest their government's actions.
"The silence from international powers with the responsibility of bringing a just settlement of the Israel-Palestine conflict must end.
"The UK Government must support the UN secretary-general's call for an independent international inquiry into the killing of protesters in Gaza and review the sale of arms that could be used in violation of international law.
"The events in Gaza and the threat of renewed conflict underlines the urgent necessity of genuine negotiations to achieve a viable two-state settlement that delivers peace, justice and security to both Palestinians and Israelis."