Donald Trump’s former national security adviser Mike Waltz has faced scrutiny from US senators over his role in a sensitive Signal group chat in which officials discussed sensitive war plans.

Waltz appeared before a hearing on Tuesday seeking Senate confirmation as Trump’s nominee for ambassador to the United Nations, following his removal from his former post in May.

Under questioning from Democrats, Waltz maintained he did not share classified information in the chat, which accidentally included a journalist.

The March incident, which became known as “Signalgate”, threw the White House into turmoil and sparked a debate about the administration’s cybersecurity.

Waltz convened the group chat on Signal that also included Secretary of Defence Pete Hegseth, Vice President JD Vance, and Secretary of State Marco Rubio, as well as several other top administration officials to discuss an imminent strike on the Houthi rebel group in Yemen.

The editor-in-chief of the Atlantic magazine, Jeffery Goldberg, was also added to the highly sensitive chat and ultimately reported on his participation, and the chat’s contents.

Amid the fallout, Waltz appeared on Fox News to take “full responsibility” for building the group chat, adding that it was “embarrassing”. Waltz and the White House have maintained no classified information was shared in the chat.

Waltz was removed from his post in May by Trump who nominated him for US ambassador to the UN.

Despite opposition from some Democrats, he will likely be confirmed since Republicans hold a majority in the US Senate.

At the hearing before the Senate Foreign Relations Committee, Senator Chris Coons, a Democrat from Delaware, said he hoped to hear Waltz express “regret over sharing what was very sensitive, timely information about a military strike on a commercially available app.”

Signal was not “an appropriate, secure means of communicating highly sensitive information,” Senator Coons said.

“That engagement was driven by and recommended by the Cyber Security Infrastructure Security Agency, by the Biden administration,” Waltz responded. He argued that the use of Signal was “not only authorised” but “highly recommended.”

“This was demonstrably sensitive information,” Senator Coons said, and asked Waltz if he was investigated for the expansion of the Signal group to include a journalist.

“The White House conducted an investigation and my understanding is the Department of Defence is still conducting an investigation,” Waltz responded.

Senator Tim Kaine, a Democrat from Virginia, also asked Waltz whether the Pentagon investigations into Secretary Hegseth were ongoing.

Waltz responded that he should not, and could not, comment on an ongoing investigation but maintained no classified information was shared.

In contrast, Waltz’s fellow Republicans on the committee largely avoided the Signal matter, instead focusing on US funding to the United Nations and asking how he would engage with China’s rising influence.

Senator Rick Scott, a Florida Republican who once served alongside Waltz in the US House of Representatives, called him a “man of integrity, grit, and principle.”

Waltz’s nomination to be the US’s lead envoy at the UN comes amid international uncertainty about America’s role on the world stage and the strength of its commitments to foreign allies.

The position would play a key role in representing US interests abroad at a time when the Trump administration has slashed billions in foreign aid and fired thousands of staffers at the State Department and US Agency for International Development (USAID).

Senator Mike Barrasso, a Wyoming Republican, asked Waltz about his “commitment to reviewing every dollar going to the UN to ensure our taxpayer dollars are being used wisely.”

In response, Waltz listed a series of international organisations and projects that he said the US helped fund that he believed deserved review, including several climate-focused entities like the UN Environment Programme, the International Union for Conservation of Nature, the Commission for Environmental Cooperation, and more.

“I think it is incumbent on this administration to say, what’s it doing, is it making us safer, stronger, and more prosperous, and are we getting enough bang for our buck,” Waltz said.