US President Donald Trump’s decision to dismiss National Security Adviser Mike Waltz last week was driven in part by deepening frustration over Waltz’s hawkish stance on Iran and his behind-the-scenes coordination with Israeli Prime Minister Benjamin Netanyahu, according to a Washington Post report published Saturday.

Citing multiple senior officials and presidential advisers, the report claims Trump had grown increasingly irritated with Waltz’s push for military action against Iran—especially as the White House was actively pursuing renewed diplomatic engagement with Tehran. Tensions reportedly peaked after it emerged that Waltz had worked closely with Netanyahu’s team ahead of a February meeting at the White House to explore joint strike options against Iran’s nuclear infrastructure.

The incident added to existing friction. Waltz had already faced internal criticism over “Signalgate,” in which he mistakenly added The Atlantic’s editor to a private chat discussing sensitive US military planning for Yemen. Though that scandal publicly embarrassed the administration, sources told the Post that the Iran dispute—not the tech mishap—ultimately sealed his fate.

Following Waltz’s ouster, Trump appointed Secretary of State Marco Rubio as interim national security adviser, making Rubio the first person since Henry Kissinger to hold both posts simultaneously. Trump also nominated Waltz to serve as the next US ambassador to the United Nations.