Marie Yovanovitch, the former US ambassador to Ukraine, has given a devastating account of the state department in “crisis” saying “the policy process is visibly unravelling” and the agency is being “hollowed” out.

Yovanovitch, who was addressing the house committees holding impeachment hearings, also delivered an indictment of “the failure of state department leadership to push back as foreign and corrupt interests apparently hijacked our Ukraine policy”.

While the impeachment proceedings are focused on the presidency, profound problems within the state department are also coming under scrutiny, as is the waning of US diplomatic clout around the world. Although she did not use his name, Yovanovitch’s opening statement amounted to a searing critique of secretary of state Mike Pompeo’s qualities as a leader.

Since being removed from her post prematurely on Trump’s orders, Yovanovitch has become a heroine for state department staff, many of whom feel let down by their leadership for failing to push back against a White House which has dismissed diplomats as “radical unelected bureaucrats”.

Those sentiments are likely to have been deepened by Trump’s tweet smearing Yovanovitch during the hearing, suggesting she was somehow responsible for chaos in Somalia, where she served early in her career.

As the ousted ambassador addressed the House committees, former and current diplomats praised Yovanovitch and the foreign service (FS) on Twitter under the hashtag #FSproud, which was promoted by the American Foreign Service Association.

An emotional Yovanovitch, who sometimes appeared close to tears, aired long-held grievances of foreign service officers about political insinuations that they are an unaccountable elite.

“There is a perception that diplomats lead a comfortable life throwing dinner parties in fancy homes. Let me tell you about some of my reality. It has not always been easy. I have moved 13 times and served in seven different countries, five of them hardship posts,” she said, recounting occasions when she had come under fire.

She spoke about feeling undermined and threatened as the president’s son Donald Trump Jr, and Trump’s lawyer, Rudy Giuliani, spread smears against her.

“If our chief representative is kneecapped, it limits our effectiveness to safeguard the vital national security interests of the United States,” she said. “Our Ukraine policy has been thrown into disarray, and shady interests the world over have learned how little it takes to remove an American ambassador who does not give them what they want,” Yovanovitch added.

“After these events, what foreign official, corrupt or not, could be blamed for wondering whether the ambassador represents the president’s views?” Yovanovitch then turned to the role of her superiors in the state department.

“I remain disappointed that the department’s leadership and others have declined to acknowledge that the attacks against me and others are dangerously wrong,” she said. “As foreign service professionals are being denigrated and undermined, the institution is also being degraded. This will soon cause real harm, if it hasn’t already.

“Moreover, the attacks are leading to a crisis in the state department as the policy process is visibly unravelling, leadership vacancies go unfilled, and senior and mid-level officers ponder an uncertain future and head for the doors,” Yovanovitch said.

In apparent response, Trump tweeted: “We have vacancies in various departments because we do not want or need as many people as past administrations (and save great cost), and also, the Democrats delay the approval process to levels unprecedented in the history of our Country!”

Widespread vacancies in key ambassadorial posts and decision-making roles have hindered the state department’s ability to function properly. Foreign diplomats in Washington regularly complain that many of their US counterparts have left the department and been replaced with officials in an acting capacity without authority to make decisions.

Pompeo has sought to keep a low profile over the Ukraine scandal, dismissing it as background “noise”. He has spent an increasing amount of time in his home state of Kansas, and giving interviews to Kansan media, adding fuel to speculation about a future Senate run.

State department diplomats are growing increasingly restive and cynical about his promotion of buzzwords like “swagger” and his “one team, one mission” ethos.

“It is very reminiscent of the army ‘creed’ which he probably remembers from his time at West Point in the army,” a senior American diplomat said. “There is an apparent contradiction between the ethos and how he has behaved towards his own ambassadors and officials.”