The fiancée of Saudi journalist Jamal Khashoggi has called for those responsible for his murder to be brought to justice, adding that she declined an invitation by US President Donald Trump to visit the White House.Hatice Cengiz, a Turkish national, made the comments in an emotional interview with broadcaster Haberturk on Friday, her first TV appearance since Khashoggi's killing inside the kingdom's consulate in Istanbul more than three weeks sgo."I demand that all those involved in this savagery from the highest to the lowest levels are punished and brought to justice," she said.Khashoggi, a Washington Post columnist and critic of Saudi Arabia's government, walked into the main entrance of the Saudi consulate at 13:14 on October 2 to obtain paperwork for his upcoming marriage.Cengiz said she waited outside the consulate for Khashoggi for more than 10 hours. But he never re-emerged. Saudi Arabia denied any knowledge of Khashoggi's fate for more than two weeks, before claiming he was killed accidentally in a fight at the consulate. On Thursday, officials changed the kingdom's account again, saying the murder appears to have been premeditated.Khashoggi's killing has spiralled into a major crisis for Saudi Arabia and its powerful Crown Prince Mohammed bin Salman, with the kingdom's shifting narrative being met with skepticism in Turkey and other parts of the world. Amid increasing international demands for accountability, Trump has vowed "severe punishment" if the Saudi government was found to be involved in the killing. He also said Saudi authorities had staged the "worst cover-up ever" over the case. In her interview with the Turkish broadcaster, Cengiz said Trump has invited her to visit the White House, but said she would not go until the US was sincere in its efforts to uncover the truth behind Khashoggi's killing. Referring to Trump's invitation, she said: "I perceived it as a statement to win public favour".'Darkness I cannot express' Cengiz broke down in tears more than once as she spoke about Khashoggi, whom she described as a "patriot". "I found myself in a darkness I cannot express," she said, describing the aftermath of Khashoggi's disappearance and death.She told Haberturk she never would have let Khashoggi enter the consulate if she had thought that Saudi "authorities would hatch a plot" to kill him.Khashoggi was not worried as he entered the building on October 2, she said, because he was treated well during a first visit to the consulate on September 28. He also assumed Saudi authorities would not give him problems or arrest him in Turkey, she said."His local network in Turkey was very good, as you know, his political network as well," Cengiz told Haberturk. "He thought Turkey is a safe country and if he would be held or interrogated, this issue would be swiftly solved."She said that she had not been contacted by Saudi officials and added she was unlikely to go to Saudi Arabia for a possible funeral if Khashoggi's missing body is found. Al Jazeera's Charles Stratford, reporting from Istanbul, said Cengiz's interview could be part of "Turkey's very well-choreographed effort to put more pressure on the Saudis". Her account suggested "a plan had been put in place to lure him back to the embassy," he added.Cengiz's television appearance came hours after Turkish President Recep Tayyip Erdogan announced the Saudi chief prosecutor will visit Istanbul on Sunday as part of the investigation into Khashoggi's death.Speaking in Ankara, Erdogan, who has so far stopped short of directly blaming the Saudi government, called on Riyadh to reveal who ordered the killing and the whereabouts of Khashoggi's body.He also said Turkey has other "information and evidence" about the killing, which it will release "when the time is right".