United States Secretary of State Mike Pompeo on Monday denied Washington was "covering up" the killing of Saudi journalist Jamal Khashoggi and promised further action.

"America is not covering up for a murder," Pompeo told reporters in Budapest when asked about criticism by a senior Democrat.

The remarks came after US President Donald Trump missed a deadline set by Congress to reply by Friday on whether Saudi Arabia's powerful Crown Prince Mohammed bin Salman ordered the killing of the Washington Post contributor.

Pompeo said that Trump's administration was "working diligently" on its investigation.

"The president has been very clear — couldn't be more clear — as we get additional information, we will continue to hold all of those responsible accountable," he said.

Khashoggi, who lived in the US, was strangled to death and dismembered in October after entering the Saudi consulate in Istanbul to take care of paperwork for his marriage, according to officials.

Trump said nothing on the congressional deadline, while congressional aides said that Pompeo had sent them a letter in which he outlined actions over the killing.

The administration revoked the visas of nearly two dozen Saudi officials and froze the assets of 17 others.

But Trump has openly said that he does not care if Prince Mohammed was responsible for the killing as Saudi Arabia buys weapons from the United States and shares his hard line on Iran.