The United States will give ally Saudi Arabia "a few more days" to probe its alleged murder of journalist Jamal Khashoggi, Secretary of State Mike Pompeo said on Thursday, again delaying a US response to the mounting scandal.Pompeo, who reported earlier to President Donald Trump on his trip to Saudi Arabia and Turkey, told journalists at the White House that the Saudis assured him "they will conduct a complete, thorough investigation.""I told President Trump this morning we ought to give them a few more days to complete that, so that we too have a complete understanding of the facts," Pompeo said.Only then, Pompeo said, "we can make decisions how or if the United States should respond."Trump has come under fire from members of Congress for his repeated delays in forming a response, as evidence mounts that Khashoggi, a US resident and Washington Post columnist, was killed and dismembered by Saudi agents inside the Saudi consulate in Istanbul more than two weeks ago.A former regime insider, Khashoggi had become a critic of powerful Crown Prince Mohammed bin Salman, the point man in ever-tightening military and commercial relations between the Muslim petro-state and the Trump administration.Call for UN probeFour prominent human rights and press freedom groups on Thursday urged Turkey to request a United Nations investigation to prevent a "whitewash" of the alleged crime.The Committee to Protect Journalists, Human Rights Watch, Amnesty International and Reporters Without Borders said such a probe established by UN Secretary-General Antonio Guterres would finally clear up the affair.But the United States, the Saudis' most powerful patron, has been in no rush to escalate the scandal.Repeatedly giving the Saudi royals the benefit of the doubt, Trump and top officials have instead stressed that the US-Saudi relationship is too important to put at risk.Trump has repeatedly praised massive Saudi arms purchases, while Pompeo used much of his brief remarks on Thursday to recall Washington's "long strategic relationship with the kingdom of Saudi Arabia."The Saudis "continue to be an important counter-terrorism partner, they have custody of the two holy sites ... We need to be mindful of that as well," he said.International fallout hits princeThe furore has also blown a hole in next week's Future Investment Initiative conference in Riyadh, which was meant to showcase Prince Mohammed's plans for modernizing the desert kingdom.US Treasury Secretary Steven Mnuchin announced he was pulling out, joining senior ministers from Britain, France and the Netherlands, as well as a string of corporate leaders.Russian President Vladimir Putin, meanwhile, took a dig at Washington, saying that "the US holds a certain responsibility over what happened to him."But he said Moscow would not "start deteriorating relations" with Saudi Arabia as long as "it did not know what really happened."Gory detailsNeither Turkey nor the United States has publicly confirmed that Khashoggi is dead or said officially that Riyadh is to blame.But a steady stream of unconfirmed leaks from officials to Turkish media have painted a detailed and horrifying picture of Khashoggi's last minutes, allegedly at the hands of 15 Saudi agents waiting for him when he came to the consulate for paperwork.The pro-government Yeni Safak newspaper on Wednesday claimed it had heard audio tapes in which Khashoggi's alleged killers tortured him by cutting his fingers off before his decapitation.The pro-government Sabah newspaper on Thursday said Saudi security official Maher Abdulaziz Mutreb, believed to be close to the crown prince, was the leader of the operation."Here is the head of the execution team," said Sabah's headline, and the paper then detailed Mutreb's movements on the day Khashoggi went missing.Giving precise times based on CCTV footage, the newspaper reported that Mutreb went into the consulate more than three hours before Khashoggi entered the building. In a series of CCTV images, Mutreb was then seen outside the consul's residence, then later at his hotel near the Saudi mission with a "large suitcase", and finally at the airport in the early evening.