US Attorney General Merrick Garland promises Justice Department won’t let voters get intimidated ahead of midterms

"I am devastated that I caused hurt to past and present colleagues by the way in which I have spoken to them," Lander wrote in his resignation letter.

"I have sought to push myself and my colleagues to reach our shared goals -- including at times challenging and criticizing," he added, acknowledging he "crossed the line at times into being disrespectful and demeaning."

Lander was named director of the Office of Science and Technology Policy in January last year under Biden, who elevated the White House science advisor position to cabinet-level -- a break from the policy of former president Donald Trump as America grappled with the Covid-19 pandemic.

Biden, a Democrat, had also set out to distinguish his administration from that of his Republican predecessor's by pledging to safeguard a respectful and professional work environment.

Lander resigned after an internal White House review sparked by a complaint filed last year found "credible evidence" the top scientist was "bullying" toward multiple staff members, Politico reported.

Lander was leading on Biden's cancer "moonshot" initiative, relaunched this month with a goal of cutting the US death rate from the disease by half.

Biden expressed thanks for Lander's work on the Covid-19 "pandemic, the Cancer Moonshot, climate change, and other key priorities," and knows he "will continue to make important contributions to the scientific community," press secretary Jen Psaki said.