Saudi Foreign Minister Adel al-Jubeir insisted Sunday that the killing was "a tremendous mistake" - part of a "rogue operation," he said - and the crown prince had not ordered it.
"This was an operation where individuals ended up exceeding the authorities and responsibilities they had".
Saudi officials originally said Khashoggi, who entered the diplomatic mission on October 2, had left unharmed, before announcing Friday that he was killed inside the building in what they described as an altercation. "That is unacceptable in any government", al-Jubeir said on Sunday.
"Nothing can justify this killing and we condemn it in the strongest possible terms", Germany, Britain and France said in their joint statement.
"We're trying to ascertain the facts as to what happened in the consulate", he said. "We are determined to uncover every stone.We are determined to punish those who are responsible for this murder".
Saudi Arabia said 18 Saudi suspects were in custody and intelligence officials had been fired.
Reuters on Sunday quoted an unnamed Saudi official who portrayed Khashoggi's death as the result of a botched kidnapping.
In an interview with the Washington Post published late Saturday, Trump stepped back from his stance that Saudi Arabia's latest explanation for the death of the journalist inside their Istanbul consulate was credible, but said he remained confident in the leadership of Crown Prince Mohammed bin Salman.
California Rep. Adam Schiff, the top Democrat on the House intelligence committee, said on ABC's "This Week" that the killing should be a "relationship-altering" event for the USA and Saudi Arabia, which has said it will retaliate against any economic sanctions or other moves against it.
Saudi Arabia's Attorney General confirmed that preliminary investigations indicated that the journalist died inside the Saudi consulate after a fight within the premises. "On the other hand you cannot teach a 33-year-old crown prince that he can get away with things that have this outrageous and stupid or he will be out of control for the next 40 years".
Separately, SPA also reported that Crown Prince Mohammad bin Salman made a telephone call to Salah Khashoggi, in which the Crown Prince expressed his condolences to Salah and his family on the death.
Meanwhile, Turkish President Recep Tayyip Erdogan said that he will make statements about the murdered journalist during his party's parliamentary group meeting on Tuesday.
"We seek justice and this will be revealed in all its naked truth, not through some ordinary steps but in all its naked truth", Erdogan said on Sunday, according to the semiofficial Anadolu news agency.
Saudi Arabia faced a growing chorus of incredulity on Sunday, with world powers demanding answers. "All of this needs to be explained in all its details", Erdogan said. In a detailed account, the official said members of the 15-man Saudi team threatened to drug and kidnap Khashoggi and had "killed him in a chokehold" when he resisted.