A top White House aide has defended Donald Trump’s disparaging tweets about an influential black Democratic congressman and his district as a “justified response to the politician’s criticism of the US president’s border policies.

Acting chief of staff Mick Mulvaney said Mr Trump was upset over what he perceives to be inaccurate statements by Elijah Cummings about conditions in which children are being held in detention at the border with Mexico.

Mr Mulvaney told Fox News Sunday that “when the president hears lies like that, he’s going to fight back”.

At a hearing last week, Mr Cummings, who represents Balitmore in Maryland, accused a top US administration official of wrongly calling reports of filthy, overcrowded border facilities “unsubstantiated”.

Mr Mulvaney denies that Trump’s Twitter comments Saturday were racist and says Mr Trump would criticise any lawmaker who spoke unfairly about his policies.

Mr Trump lashed out in tweets against Mr Cummings, the powerful House Oversight Committee chairman, claiming his Baltimore-area district is “considered the worst run and most dangerous anywhere in the United States”.

It was the president’s latest assault on a prominent politician, and the people he represents, two weeks after he sparked nationwide controversy with tweets directed at four congresswomen.

His comments against Mr Cummings, who leads multiple investigations of the president’s governmental dealings, drew swift condemnation from Democrats.

Statements from a spokesman for the state’s Republican governor and from the lieutenant governor defended Mr Cummings’s district and its people.

Mr Trump called Mr Cummings a “brutal bully” after his public tongue-lashing of top Homeland Security officials over conditions for migrants detained along the southern border.

“As proven last week during a Congressional tour, the Border is clean, efficient & well run, just very crowded,” Mr Trump tweeted.

“Cumming District is a disgusting, rat and rodent infested mess.”

Mr Cummings replied directly to Mr Trump on Twitter, saying, “Mr President, I go home to my district daily. Each morning, I wake up, and I go and fight for my neighbors. It is my constitutional duty to conduct oversight of the Executive Branch. But, it is my moral duty to fight for my constituents.”

Mr Cummings has also drawn the president’s ire for investigations touching on his family members serving in the White House.

On Thursday his committee voted along party lines to authorise subpoenas for personal emails and texts used for official business by top White House aides, including Ivanka Trump and her husband, Jared Kushner.