President Joe Biden has said he is unsure whether Israel’s Prime Minister Benjamin Netanyahu is holding off on agreeing a Gaza ceasefire deal in order to influence next month’s US election.

He was asked the question during a surprise appearance at a White House press briefing on Friday, telling reporters: “Whether he’s trying to influence the election, I don’t know – but I’m not counting on that.”

Biden then directed some terse words at his longtime ally: “No administration has helped Israel more than I have. None, none, none,” he said. “And I think [Netanyahu] should remember that.”

Some Democrats have voiced concern that Netanyahu is ignoring the US president’s calls to negotiate a ceasefire and hostage release deal in order to harm the party’s chances in November.

Earlier this week, Democratic Senator Chris Murphy told CNN: “I don’t think you have to be a hopeless cynic to read some of Israel’s actions, some of Prime Minister Netanyahu’s actions, as connected to the American election.”

Polls suggest the escalating violence in the Middle East and the failure to secure a diplomatic agreement is hurting Biden and his replacement as the Democratic candidate, Kamala Harris.

The president’s approval rating among Arab-Americans has plummeted over the past year, largely due to anger at US support for Israel’s military campaign, and this could damage the party’s prospects in November.

Biden has been pushing for a diplomatic agreement between Israel and Hamas for months, and has indicated several times that one is close. A deal before the election would be a major boost for the president and the Democratic Party but appears increasingly unlikely.

While the Biden administration has mostly criticised Hamas for failing to reach an agreement, the president has also expressed increasing public frustration with Netanyahu, who he recently said was not doing enough to strike a deal.

Netanyahu, meanwhile, has rejected suggestions from Washington that an agreement is close.

“Hamas is not there with a deal. There’s not a deal in the making, unfortunately,” the Israeli prime minister said earlier this month just hours after a US official said it was 90% complete.

The increasingly fractious relationship between Biden and Netanyahu, who have known one another for decades, contrasts with the friendly relationship the Israeli leader had with former president Donald Trump, the current Republican nominee.

Israel, meanwhile, has continued strikes on Gaza and pushed ahead with a ground invasion in southern Lebanon. It has also vowed to respond to an Iranian ballistic missile attack this week.

At his appearance at Friday’s press briefing, which came as a shock to reporters in the room as it was his first since becoming president four years ago, Biden responded to concern that Israel could strike Iranian oil fields in retaliation.

“The Israelis have not concluded what they are going to do in terms of a strike,” he said. “If I were in their shoes, I’d be thinking about other alternatives than striking oil fields.”

Biden caused oil prices to rise on Thursday when he said the US was discussing with Israel the possibility of strikes on Iran’s oil infrastructure.