US Defense Secretary Jim Mattis said on Saturday that the killing of Saudi journalist Jamal Khashoggi undermined Middle Eastern stability and that Washington would take additional measures against those responsible.
Washington Post columnist Khashoggi's murder has escalated into a crisis for the world's top oil exporter. Saudi Arabia's allies have reacted with outrage towards a country that is the lynchpin of a US-backed regional bloc against growing Iranian influence in the Middle East.
But Mattis also said U.S. respect for the Saudi people was undiminished, while Saudi Foreign Minister Adel al-Jubeir said those behind the killing would be prosecuted in the kingdom and that the investigation would take time.
US President Donald Trump has said he wants to get to the bottom of the case, while also highlighting Riyadh's role as an ally against Tehran and Islamist militants, as well as a major purchaser of US arms.
"With our collective interests in peace and unwavering respect for human rights in mind, the murder of Jamal Khashoggi in a diplomatic facility must concern us all greatly," Mattis told a conference in Bahrain.
"Failure of any one nation to adhere to international norms and the rule of law undermines regional stability at a time when it is needed most," Mattis said. He did not mention de facto Saudi ruler Crown Prince Mohammed bin Salman by name at any point.
Saudi Arabia's public prosecutor said Khashoggi's killing was premeditated, contradicting a previous official statement that it happened accidentally during a tussle in the Saudi consulate in Istanbul.
Saudi officials have also said he was accidentally killed in a botched security operation to return him to the kingdom.