Hamas on Sunday slammed Israel's suspension of supplies and aid entering Gaza, describing it as a "war crime" and a violation of the ceasefire agreement.

Israeli Prime Minister Benjamin Netanyahu's "decision to suspend humanitarian aid is cheap blackmail, a war crime and a blatant coup against the (ceasefire) agreement", the group said in a statement.

Israel announced earlier on Sunday that it was suspending the entry of supplies into Gaza, and threatened "consequences" for Hamas if it did not accept a proposal for a temporary extension of the truce in the Palestinian territory.

"Prime Minister Benjamin Netanyahu decided that, from this morning, all entry of goods and supplies into the Gaza Strip will be suspended," his office said in a statement.

"Israel will not accept a ceasefire without the release of our hostages. If Hamas persists with its refusal, there will be other consequences."

The first phase of the Israel-Hamas ceasefire, which included a surge in humanitarian assistance, expired on Saturday.

The two sides have yet to negotiate the second phase, in which Hamas was to release dozens of remaining hostages in return for an Israeli pullout and a lasting ceasefire.

Israel said earlier on Sunday that it supported a proposal to extend the first phase of the ceasefire through Ramadan and Passover, or April 20.

It said the proposal came from the Trump administration's Mideast envoy, Steve Witkoff.

Under that proposal, Hamas would release half the hostages on the first day and the rest when an agreement is reached on a permanent ceasefire, according to Israeli Prime Minister Benjamin Netanyahu's office. (Agencies)