Former Secretary of State Rex Tillerson has warned of “a growing crisis of ethics and integrity” in the US, in an apparent rebuke of President Donald Trump.

While Mr Tillerson did not mention Mr Trump by name in his first public remarks since leaving his administration, he told graduates at the Virginia Military Institute in Lexington: “If our leaders seek to conceal the truth, or we as people become accepting of alternative realities that are no longer grounded in facts, then we as American citizens are on a pathway to relinquishing our freedom”.

He also warned that if Americans fail to address the ethics crisis now, it could mean “American democracy as we know it is entering its twilight years”.

The former Exxon executive was critical of leaders who encouraged a society “based on wishful thinking ... [and] hoped-for outcomes made in shallow promises”.

One other line stuck out for Washington insiders as a thinly-veiled critique of Mr Trump: “We do not have to look far to find examples of the cost to individuals and to society when integrity is sacrificed for immediate gain or personal achievement,” the former top diplomat said.

While cautioning the graduates about the US alienating its longtime allies, he also noted that globalisation and trade – issues Mr Trump has railed against as part of his ‘America First’ foreign policy – are not inherently bad for the future of the American workforce.

Rex Tillerson gives statement after being fired as Secretary of State

He acknowledged that trade has “led to anxiety and fear” jobs leaving the country but said that “every nation has the right to aspire to a better quality of life, and that free trade and economic growth are the means by which economic opportunity is created for all people”.

Mr Trump has used the word “unfair” to describe nearly every multilateral or bilateral deal the US is party to, particularly the North American Free Trade Agreement (Nafta) with Canada and Mexico.

Donald Trump sacks Rex Tillerson

Mr Tillerson also said that the “damage” done by a lack of “public trust” in certain institutions and individuals at the top “strikes at the very heart of a free society”.

The president and Mr Tillerson’s relationship appeared to sour after rumours surfaced that the Texan had called Mr Trump a “moron” during a meeting at the Pentagon in July 2017, a report the State Department denied at the time. Mr Tillerson himself never formally denied the remark but said he would not deal with such "petty nonsense"

Mr Tillerson's departure from the State Department was announced by Mr Trump in a tweet back in March.

Mr Trump told reporters in the wake of that tweet announcing his nomination of former CIA Director Mike Pompeo for the top diplomatic post, that he and Mr Pompeo shared similar thinking and he had “disagreed” with Mr Tillerson. Mr Trump added that the former oil and gas CEO would be “much happier” out of office.

The pair had reportedly butted heads on matters involving Russia and North Korea in particular. In October 2017, the president had tweeted that Mr Tillerson was ”wasting his time“ trying to negotiate with North Korean leader Kim Jong-un through State Department diplomatic backchannels. At the time Mr Trump had warned of raining down “fire and fury” on Pyongyang in light of its development of nuclear weapons.