President Joe Biden warned Israel of a sharp shift in his policy over the Gaza conflict Thursday amid growing frustration with Benjamin Netanyahu and mounting domestic pressure in a US election year, AFP reports.

A tense phone call between the two leaders appeared to yield at least some results, as Netanyahu’s office announced within hours it would temporarily allow more aid to flow into Gaza.

But the Democrat faces spiraling anger from Muslim and younger voters over his support for Israel, and political allies have been pressing him to make the aid conditional on changed Israeli behavior.

In a 30-minute call with Netanyahu after Israeli strikes killed seven aid workers from US-based charity World Central Kitchen, Biden hinted at doing just that.

For the first time, Biden “made clear that US policy with respect to Gaza will be determined by our assessment of Israel’s immediate action” to curtail the killing of civilians and aid workers and improve the dire humanitarian situation, the White House said.

The tough language, describing the aid worker attack as “unacceptable” and urging Israel to take steps towards an immediate ceasefire, reflected mounting tensions with Netanyahu.

“What happened to the World Central Kitchen, that event certainly was a catalyst for the call today,” White House National Security Council spokesman John Kirby told CNN Thursday evening.