Saudi Arabia on Saturday admitted that critic Jamal Khashoggi was killed during a "brawl" inside its Istanbul consulate, an explanation that President Donald Trump said he found credible but failed to convince top US lawmakers.The kingdom announced the arrest of 18 Saudis in connection with their probe and the sacking of two top officials linked to Crown Prince Mohammed bin Salman who has faced mounting pressure over the Khashoggi affair.Khashoggi, a critic of the Islamic petro-state's powerful crown prince and a Washington Post contributor, was last seen on October 2 entering his country's consulate in Istanbul.His disappearance had been shrouded in mystery and triggered an international crisis, with Turkish officials accusing Saudi Arabia of a state-sponsored killing and dismembering his body.The admission of his death after vehement denials by the Gulf kingdom came amid threats of US sanctions and leaves lingering questions about whether Prince Mohammed had any role in the affair.In the latest version of events from Riyadh, Saudi Attorney General Sheikh Saud al-Mojeb said Khashoggi died after "discussions" at the consulate devolved into an altercation, without disclosing any details on the whereabouts of his body."Discussions that took place between him and the persons who met him... at the Saudi consulate in Istanbul led to a brawl and a fist fight with the citizen, Jamal Khashoggi, which led to his death, may his soul rest in peace," the attorney general said in a statement.The Saudi king also ordered the setting up of ministerial committee under the chairmanship of the crown prince, widely known as MBS, to restructure the kingdom's intelligence agency and "define its powers accurately", state media said.Deputy intelligence chief Ahmad al-Assiri and royal court media advisor Saud al-Qahtani, both top aides to Crown Prince Mohammed bin Salman, were sacked. 'Intense outcry'The controversy has put the kingdom - for decades a key Western ally and bulwark against Iran in the Middle East - under unprecedented pressure to offer an explanation to take the heat off its rulers.It evolved into a major crisis for Prince Mohammed, a US administration favourite whose image as a modernising Arab reformer has been gravely undermined.In his first reaction, US President Donald Trump said Friday that he found credible Saudi Arabia's assertion that Khashoggi died as a result of a fight."I do, I do," Trump said when asked if the Saudis' explanation was credible, while adding: "It's early, we haven't finished our review or investigation."Trump had earlier said Washington could impose sanctions, but his administration had been notably slow to criticise the Gulf ally despite mounting evidence of what happened to Khashoggi.The case has presented Trump with one of the most acute foreign policy crises of his nearly two-year-old presidency."It took an intense international outcry sustained for two weeks to acknowledge the obvious -- that Khashoggi is dead, that he was killed in the Saudi consulate," said Kristin Diwan, of the Arab Gulf States Institute in Washington."That gives you an idea of the immense financial and strategic interests that are invested in maintaining the US partnership with Saudi Arabia and its leadership."'Deeply troubled'Saudi officials have roundly denied that Prince Mohammed had any involvement.But a suspect identified by Turkey in the disappearance of Khashoggi was said to be a frequent companion of Prince Mohammed, three others were linked to his security detail and a fifth is a high-level forensic doctor, according to The New York Times.Complicating the official narrative, Ali Shihabi, head of pro-Saudi think tank Arabia Foundation which is said to be close to the government, tweeted that "Khashoggi died from a chokehold during a physical altercation, not a fist fight", citing a senior Saudi source.Pro-government Turkish media have repeatedly claimed that Khashoggi was tortured and decapitated by a Saudi hit squad inside the diplomatic mission, although Turkey has yet to divulge details about the investigation."Each successive narrative put out by the Saudis to explain what happened to Khashoggi has strained credulity," Kristian Ulrichsen, a fellow at Rice University's Baker Institute in the United States, told AFP."Especially because the Saudis are still unable or unwilling to produce the one piece of evidence - a body - that could provide a definitive answer one way or the other."UN chief Antonio Gutterres said he was "deeply troubled" by the kingdom's disclosure on Saturday, adding there needed to be "full accountability for those responsible."Republican Senator Lindsey Graham, an influential US Senate ally of President Donald Trump, called for the ouster of the crown prince. "This guy is a wrecking ball. He had this guy murdered in a consulate in Turkey," Graham told "Fox and Friends". Bob Menendez, the top Democrat on the Senate Foreign Relations Committee, called for sanctions.Shortly before Riyadh confirmed Khashoggi's killing, Turkey's President Recep Tayyip Erdogan and Saudi King Salman agreed in telephone talks to continue cooperation in the investigation into the Khashoggi affair.Saudi Arabia's admission comes after Turkish authorities widened their probe on Friday, searching a forest in Istanbul city.