The Iowa Republican congressman Steve King was under mounting pressure on Saturday, over remarks in which he asked how the term “white supremacy” came to be seen to be offensive.

The Congressional Black Caucus (CBC) called for the immigration hardliner and Trump ally to be stripped of committee assignments.

In a piece about immigration published on Thursday, the New York Times quoted King as saying: “White nationalist, white supremacist, western civilization. How did that language become offensive?”

On Friday, King sought to explain himself on the floor of the House, saying: “One phrase in that long article has created an unnecessary controversy. That was my mistake.”

He also said the interview “was [a] discussion of other terms that have been used, almost always unjustly labeling otherwise innocent people. The word racist, the word Nazi, the word fascist, the phrase white nationalists, the phrase white supremacists.”

King said he had been wondering aloud: “How did that offensive language get injected into our political dialogue? Who does that, how does it get done, how do they get by with laying labels like this on people?”

It was not clear if Republican leadership would actually move to formally censure King, but politicians from both parties expressed disdain for the nine-term representative’s latest inflammatory remarks.

In a column for the Washington Post, the Republican South Carolina senator Tim Scott, who is black, wrote: “When people with opinions similar to King’s open their mouths, they damage not only the Republican party and the conservative brand but also our nation as a whole.”

The headline on the piece was: “Why are Republicans accused of racism? Because we’re silent on things like this.”

On Saturday, the CBC chair Karen Bass, a California Democrat, tied King’s views to those of the Republican president, who last year told a rally the congressman “may be the world’s most conservative human being”.

“Like Donald Trump,” she said, “Steve King has sought again and again to give comfort to white supremacists, something that should never be allowed in the halls of Congress or the Oval Office.

“If Republicans really believe these racist statements have no place in our government, then their party must offer more than shallow temporary statements of condemnation.”

Anything less than the stripping of King’s committee assignments would represent the “tacit acceptance of racism from the Republican party”, Bass said.

King has repeatedly won re-election in Iowa’s fourth congressional district, despite regularly attracting controversy for his far-right views and associations, which stretch to Britain and Europe.

In November’s midterms, he won narrowly. This week Randy Feenstra, a Republican state senator, said he would challenge King in a primary in 2020.