Sir Keir Starmer is facing pressure from some of his own MPs to take further action against Israel over what they say is a genocide in Gaza.
At prime minister's questions, Sir Keir described the situation in Gaza as "appalling and intolerable" and repeated calls for a ceasefire.
He added that further actions against Israel will be considered, including sanctions.
But his words were not enough to satisfy opposition critics and left-wing Labour MPs, who are calling on the government to take stronger action against Benjamin Netanyahu and his ministers.
It comes after aid distribution centres in Gaza were closed for the day, with the Israeli military warning roads leading to the sites will be considered "combat zones".
At least 27 Palestinians were killed by Israeli fire close to a distribution centre on Tuesday, according to the Hamas-run Civil Defence Agency.
The Israel Defence Forces say its troops fired shots after identifying suspects who moved towards them "deviating from the designated access routes".
The UK's Middle East Minister Hamish Falconer faced the anger of backbench Labour MPs – many of whom were wearing red "stop arming Israel" badges – in the House of Commons.
Falconer said he was "appalled" by Palestinians being killed when trying to access aid sites, adding: "We call for an immediate and independent investigation into these events for the perpetrators to be held to account."
He added: "Israel's unjustified block on aid into Gaza needs to end – it is inhumane.
"Israel must immediately allow the United Nations and aid partners to safely deliver all types of aid at scale to save lives, reduce suffering and maintain dignity."
