Israel has blocked the entry of all humanitarian aid into Gaza as it demands Hamas agree to a US plan for a ceasefire extension.
The first phase of the ceasefire expired on Saturday. Israeli Prime Minister Benjamin Netanyahu's office said Hamas had so far refused to accept a temporary extension under a proposal by Donald Trump's envoy, Steve Witkoff.
A Hamas spokesman said blocking supplies to Gaza was "cheap blackmail" and a "coup" on the ceasefire agreement and urged mediators to intervene.
The Palestinian group wants phase two of the deal to go ahead as originally negotiated, with the release of hostages and Palestinian prisoners and the withdrawal of Israeli forces from Gaza.
It previously said it would not agree to any extension of phase one without guarantees from US, Qatari and Egyptian mediators that phase two would eventually take place.
A statement from Netanyahu's office said: "With the end of Phase 1 of the hostage deal, and in light of Hamas's refusal to accept the Witkoff outline for continuing talks - to which Israel agreed - Prime Minister Netanyahu has decided that, as of this morning, all entry of goods and supplies into the Gaza Strip will cease.
"Israel will not allow a ceasefire without the release of our hostages. If Hamas continues its refusal, there will be further consequences."
The Hamas spokesman said: "Netanyahu's decision to stop aid going into Gaza once again shows the ugly face of the Israeli occupation... The international community must apply pressure on the Israeli government to stop starving our people."
Late last night, Netanyahu's office said Israel had agreed to a US proposal for the ceasefire to continue for about six weeks during the Muslim Ramadan and Jewish Passover periods.
If, at the end of this period, negotiations reached a dead end, Israel would reserve the right to go back to war.
US envoy Witkoff has not made his proposal public. According to Israel, it would begin with the release of half of all the remaining living and dead hostages.
