President Donald Trump speaks in the Oval Office of the White House in Washington. Picture: Carolyn Kaster/AP

Washington - The Baltimore Sun newspaper published a scathing editorial on Sunday against President Donald Trump, defending conditions in an urban district of the eastern US city that Trump had attacked, as well as the US lawmaker who represents the district.

The daily newspaper, in an editorial titled "Better to have a few rats than to be one," pointed to the district's landmarks and a median income above the national average. The US president on Saturday called the district a "disgusting, rat and rodent infested mess" and said "no human being would want to live there".

The newspaper's editorial board said that, while it did not wish to "sink to name-calling", it would "tell the most dishonest man to ever occupy the Oval Office" that it's "better to have some vermin living in your neighborhood than to be one."

The editorial said that Trump sees attacking African American members of Congress as good politics as it "warms the cockles of the white supremacists who love him." The president was not fooling most Americans into believing "he's even slightly competent," it added.

Trump touched off the latest racially charged round of accusations with a series of tweets on Saturday in which he said Cummings had done little to help his district in more than 20 years in office.

He upped the ante on Sunday by firing off another attack, saying Cummings had "failed badly!" and not addressed crime in Baltimore because he has been too busy using the House Oversight Committee "to hurt innocent people and divide our Country!"

Cummings is chairman of the committee and is the driving force behind several investigations into the Trump administration. The 68-year-old also has denounced Trump's migration policies affecting the US-Mexico border, especially the conditions in detention centres and treatment of children separated from their parents.

Trump broadened his attack in his Sunday tweets by naming House Speaker Nancy Pelosi, who had defended Cummings on Saturday and called Trump's tweets racist.

The US president suggested someone should explain to Pelosi "that there is nothing wrong with bringing out the very obvious fact that Congressman Elijah Cummings has done a very poor job for his district and the City of Baltimore."

He also said conditions in Pelosi's district in San Francisco make it "not even recognizeable."

Neither Pelosi, who was born in Baltimore and whose father also served as mayor of the city decades ago, nor Cummings responded to Trump's comments Sunday.

Acting White House Chief of Staff Mick Mulvaney defended the president's tweets, saying they were not racist but were responses to Cummings' criticism of conditions at the southern border.

"When the president hears lies like that, he's going to fight back," Mulvaney told Fox News. "It has absolutely zero to do with race. This is what the president does. He fights, and he's not wrong to do so."

The latest furore over Trump's tweets comes after he touched off a firestorm earlier this month by criticizing four non-white congresswomen, calling them un-American and saying they should "go back" to the countries they came from.

All four are US citizens and only one of them was not born in the United States - Representative Ilhan Omar, a Muslim who arrived as a refugee from Somalia and became a naturalized US citizen.