WASHINGTON — President Donald Trump hit out at a prominent African-American critic on Saturday, calling him a "brutal bully" who should concentrate on cleaning up his "disgusting, rat and rodent infested" Baltimore district rather than criticizing the work of US immigration officers on the Mexican border.

Trump's target in a series of early morning tweets was US Representative Elijah Cummings, the Democratic chairman of the House of Representatives Oversight Committee, who has called Trump a racist and sharply criticized his immigration policies. On Thursday, the committee voted 23-16 along party lines to allow Cummings to issue subpoenas to White House officials, including Trump's daughter Ivanka Trump and son-in-law Jared Kushner, deepening a probe into potential violations of government record-keeping laws.

In his tweet, Trump, a Republican, took aim at Cummings' criticism of his administration's Mexican border policies.

"Rep, Elijah Cummings has been a brutal bully, shouting and screaming at the great men & women of Border Patrol about conditions at the Southern Border, when actually his Baltimore district is FAR WORSE and more dangerous. His district is considered the Worst in the USA......," Trump tweeted.

"(T)he Border is clean, efficient & well run, just very crowded. Cumming District is a disgusting, rat and rodent infested mess. If he spent more time in Baltimore, maybe he could help clean up this very dangerous & filthy place," he said.

In a third tweet, Trump questioned why so much money was spent on Cummings' district, which covers the downtown area of the city of Baltimore, about 40 miles (64 km) northeast of Washington, "when it is considered the worst run and most dangerous anywhere in the United States."

"No human being would want to live there. Where is all this money going? How much is stolen? Investigate this corrupt mess immediately," Trump wrote.

Last week, Cummings slammed Trump's acting Homeland Security Secretary Kevin McAleenan over conditions of US-Mexico border facilities that house migrants.

"You feel like you're doing a great job, right?" Cummings asked during a congressional hearing. "What does that mean? What does that mean? When a child is sitting in their own feces, can’t take a shower? ... None of us would have our children in that position."

Trump's attack follows his broadside two weeks ago against four congresswomen of color, which the Democratic-controlled US House of Representatives condemned as racist.

There was no immediate comment from Cummings on Trump's tweets, but the congressman sent out tweets highlighting a letter he co-signed to the president this week expressing "profound disappointment" at his failure work to lower drug prices. "It is my constitutional duty to conduct oversight of the Executive Branch. But, it is my moral duty to fight for my constituents," Cummings said in a tweet.

Cummings represents Maryland's 7th congressional district, which according to 2010 census data was 54.6 percent black, had a median household income of $51,018, and a college graduation rate of 35.7 percent.

According to the same census, Maryland was the richest state in the United States, with a median household income of $69,272. Real median household income for the United States as a whole was $49,445 in 2010. — Reuters