President Donald Trump says Saudi authorities staged the "worst cover-up ever" in the killing of journalist Jamal Khashoggi this month.
The United States has also vowed to revoke visas of some of those believed to be responsible.
Mr Trump spoke hours after Turkey's president, Tayyip Erdogan, dismissed Saudi efforts to blame Mr Khashoggi's death on rogue operatives.
Mr Erdogan urged Riyadh to search "from top to bottom" to uncover those behind Mr Khashoggi's death in the Saudi consulate in Istanbul on 2 October, an incident that has prompted global outrage and strained relations between Riyadh and Washington.
Asked by a reporter in the White House Oval Office how the Khashoggi killing could have happened, Mr Trump said: "They had a very bad original concept. It was carried out poorly, and the cover-up was one of the worst in the history of cover-ups."
Mr Khashoggi, a critic of Saudi Crown Prince Mohammed bin Salman, was a US resident and Washington Post columnist.
Mr Trump's comments in recent days have ranged from threatening Saudi Arabia with "very severe" consequences and mentioning possible economic sanctions, to more conciliatory remarks highlighting the country's role as a US ally against Iran and Islamist militants, as well as a major purchaser of US arms.
Mr Trump said the Khashoggi matter was handled badly by Saudi officials.
"Bad deal, should have never been thought of. Somebody really messed up. And they had the worst cover-up ever," Mr Trump said.
Mr Trump did not give his views on who was ultimately responsible. But Secretary of State Mike Pompeo said the United States has identified some of the Saudi government and security officials it believes were involved in Mr Khashoggi's murder and would take appropriate actions including revoking US visas.
As the crisis unfolded over the past three weeks, Saudi Arabia changed its tune on Mr Khashoggi.
Riyadh initially denied knowledge of Mr Khashoggi's fate before saying on Saturday he was killed in a fight in the consulate, an account met with skepticism from several Western governments, straining their relations with the world's biggest oil exporter.
Saudi state media said King Salman fired five officials over the killing carried out by a 15-man hit team, including Saud al-Qahtani, a top aide who ran social media for Prince Mohammed. According to two intelligence sources, Mr Qahtani ran the killing by giving orders over Skype.
King Salman, 82, has handed the day-to-day running of Saudi Arabia to the 33-year-old crown prince.
Turkish officials suspect Mr Khashoggi was killed and dismembered inside the consulate by Saudi agents. Mr Erdogan stopped short of mentioning the crown prince who some US lawmakers suspect ordered the killing.
"The Saudi administration has taken an important step by admitting to the murder. From now on, we expect them to uncover all those responsible for this matter from top to bottom and make them face the necessary punishments," Mr Erdogan said in a speech in parliament.
"From the person who gave the order, to the person who carried it out, they must all be brought to account," Turkey's president said, adding that the Saudis need to "uncover all those responsible for this matter from top to bottom."
Turkish sources have said that authorities have an audio recording purportedly documenting the killing. Mr Erdogan made no reference to any audio recording.
A Saudi cabinet meeting chaired by King Salman said Riyadh would hold to account those responsible for the killing and those who failed in their duties, whoever they were.
Turkish investigators searched a Saudi consulate vehicle in Istanbul that contained two suitcases and other items, according to broadcaster CNN Turk. It was not clear what was in the suitcases.
"I want to assure the American people: we're going to get to the bottom of it. This brutal murder of a journalist, of an innocent man, of a dissident, will not go without an American response and, I expect, without an international response," US Vice President Mike Pence said at an event hosted by The Washington Post.
Mr Trump said he would work with the US Congress to determine the US response to the Khashoggi matter.
"In terms of what we ultimately do, I'm going to leave it very much - in conjunction with me - up to Congress. And that means Congress, both Republicans and Democrats," Mr Trump said, adding that he would like a bipartisan recommendation.
CIA Director Gina Haspel, in Turkey to investigate the death of Mr Khashoggi, has sought to hear a purported audio recording of his torture and murder, four sources familiar with her mission told Reuters.
A host of Western executives and governments have pulled out of a high-profile Saudi investment summit that started on Tuesday because of the Khashoggi affair.
Mr Erdogan said the killing was planned from when Mr Khashoggi, 59, first went to the Saudi consulate in Istanbul on 28 September to obtain documents necessary for his marriage. He was told he would need to return later to collect the documents.
A day before Mr Khashoggi's death, agents arrived from overseas and began to scout locations, including the Belgrad Forest near Istanbul and the city of Yalova to its south, Mr Erdogan said. Police have searched both areas for evidence of Mr Khashoggi's remains, Reuters has reported.
On the day Mr Khashoggi arrived for his appointment and was later killed, the hard disk in the consulate's camera system was removed, Mr Erdogan said.
"Covering up a savage murder like this will only hurt the human conscience. We expect the same sensitivity from all parties, primarily the Saudi Arabian leadership," he said.
"We have strong signs that the murder was the result of a planned operation, not a spontaneous development."
On the day of the killing, 15 people went to the consulate, including security, intelligence and forensic experts, Mr Erdogan said. Consulate personnel were given the day off.
"Why did these 15 people meet in Istanbul on the day of the murder? We are seeking answers to this. Who are these people receiving orders from?" Mr Erdogan asked. He said that he wanted Saudi Arabia to send the suspects to Turkey for trial.