A deadline last Friday imposed in 2018 by 22 bipartisan senators was ignored by the White House. The lawmakers had called for an investigation into the killing of the journalist, who was allegedly strangled and dismembered in October inside a Saudi consulate in Istanbul.
The probe, which specifically directed the White House to conclude whether Saudi crown prince Mohammed Bin Salman was responsible for the murder, was requested under the Global Magnitsky Human Rights Accountability Act.
A senior administration official told Politico Donald Trump “maintains his discretion to decline to act on congressional committee requests when appropriate”.
But Marco Rubio, a Republican senator who sits on the committee, said the Trump administration’s failure to meet the deadline “violates the law”.
“The law is clear about those timelines. I’m urging them and I expect them to comply with the law,” he added.
Republican senator Cory Gardner said there was “no excuse” and that the government “must submit it”, while Chuck Grassley, an influential Republican lawmaker, said “they better have a good excuse for not issuing it”.
Over the weekend, secretary of state Mike Pompeo pushed back against allegations of a US-backed cover-up over the killing of Khashoggi, who was a prominent critic of the Saudi royal family.
"America is not covering up for a murder," he told reporters at the US embassy in Budapest.
Mr Pompeo sent on Friday a letter to Bob Menendez, the ranking Democrat on the foreign relations committee, in which he said Mr Trump had called for a prompt and open investigation into the death of Khashoggi.
Mr Pompeo wrote that in multiple meetings with Saudi officials and in numerous public statements, he had "emphasised the importance of a thorough, transparent and timely investigation, including accountability for those responsible for the killing".
He also noted the US sanctioned 17 Saudi individuals for their involvement in the killing, but the letter did not assess whether the crown prince was responsible.
Democratic senator Tim Kaine of Virginia, where Mr Khashoggi lived, accused the Trump administration of “aiding in the cover-up of a murder”.
"The Trump administration has blatantly turned a blind eye to this crime, and is now refusing to provide a required report about who is responsible for his murder, despite the fact that the CIA concluded that Crown Prince Mohammed bin Salman personally ordered Khashoggi's killing,” he said.
Mr Pompeo insisted the US would “continue our investigation” and that Mr Trump had been “very clear” that his administration would “continue to hold all of those responsible accountable”.
The CIA is reported to have assessed with “high confidence” that Mr Bin Salman was involved in the order to kill Mr Khashoggi - a claim he has vehemently denied - partly based on the judgement that as the country’s de facto ruler he would have had to have known.
But Mr Trump’s desire to maintain close relations with Saudi Arabia – including lucrative weapons deals – has seen his administration play down the agency’s assessment.