US President Donald Trump says he has accepted the resignation of scandal-plagued Environmental Protection Agency chief Scott Pruitt.

Mr Pruitt had backed the President by rolling back environmental regulations, but came under fire for a variety of ethics accusations.

He was under scrutiny for months over first-class travel at taxpayer expense, security spending, connections with lobbyists and industry groups, accusations of using his office for favours, a $US43,000 ($58,209) soundproof phone booth for his office and his rental of a high-end apartment from an energy lobbyist’s wife.

Numerous Democratic lawmakers, and even some fellow Republicans, had called for his resignation.

“I have accepted the resignation of Scott Pruitt as the Administrator of the Environmental Protection Agency,” Mr Trump said on Twitter on Friday morning (AEST).

He said EPA deputy administrator Andrew Wheeler will become acting EPA chief on Monday.

“Within the Agency Scott has done an outstanding job, and I will always be thankful to him for this,” Mr Trump said.

…on Monday assume duties as the acting Administrator of the EPA. I have no doubt that Andy will continue on with our great and lasting EPA agenda. We have made tremendous progress and the future of the EPA is very bright!

— Donald J. Trump (@realDonaldTrump) July 5, 2018

Some of the ethics accusations involved jobs for Mr Pruitt’s wife.

Emails obtained by the Sierra Club environmental group showed Mr Pruitt had an aide contact the chief executive of a fast-food chain about his wife becoming a franchise owner.

The Washington Post reported Mr Pruitt had aides try to get her a job at the Republican Attorneys General Association with a salary topping $US200,000 ($270,000).

During congressional testimony in April, Mr Pruitt was unapologetic, often blaming his staff for any agency missteps.

Lawmakers posed tough questions on a range of issues also including raises for top aides and reports of retaliation against EPA whistleblowers. Democrats accused him of endless misconduct.

Mr Pruitt, a close ally of the fossil fuel industry, also was known for questioning the human role in global climate change.

As Oklahoma’s former attorney general, he waged a legal fight against the environmental rules implemented by the agency he eventually would head.

From a policy perspective, Mr Pruitt was one of Mr Trump’s most effective cabinet members.

Mr Trump has praised Mr Pruitt for slashing regulations on the energy and manufacturing industries, including his move to repeal Democratic former president Barack Obama’s signature program to cut carbon emissions from power plants, known as the Clean Power Plan.

Mr Pruitt also was instrumental last year in lobbying Mr Trump to withdraw the US from the global 2015 Paris climate accord to combat global warming.

Democratic US Representative Gerry Connolly said after his resignation: “Scott Pruitt’s reign of venality is finally over. He made swamp creatures blush with his shameless excesses. All tolerated because Trump liked his zealotry. Shame.”