A special UN rapporteur said Thursday that the killing was "planned and perpetrated" by Saudi officials.
In October, the then top Republican and Democrat on the Senate Foreign Relations Committee invoked the Magnitsky Act, which gave the Trump administration 120 days -- until February 8 -- to determine who was behind Khashoggi's killing and to describe actions against them.
The law, which targets extrajudicial killings and torture, is named for Sergei Magnitsky, an anti-corruption accountant who died in Russian custody.
In a joint statement Thursday accompanied by a rally outside the White House, six advocacy groups including Human Rights Watch, Reporters Without Borders and the Committee to Protect Journalists urged Trump to lay out action over Khashoggi's killing and to release CIA records on the death.
"Notwithstanding public and congressional outrage and the reported findings of the CIA, the Trump administration appears to be engaged in a cover-up on behalf of the Saudi government," they wrote.
The kingdom's promises to prosecute those responsible have turned into a "sham," the groups said, with senior officials resigning rather than facing repercussions.
But Trump also said in a blunt statement that the killing was not worth jeopardising the alliance with Saudi Arabia, crediting the kingdom with buying US weapons and supporting its hard line on regional rival Iran.