Germany has imposed European travel bans on 18 Saudi nationals suspected of involvement in the murder of Jamal Khashoggi, and confirmed its arms embargo against the regime in Riyadh.

The measures were announced by the German foreign minister, Heiko Maas, who told reporters in Brussels that the travel ban covered the 26-nation Schengen zone and had been issued in close coordination with France, which is part of the Schengen area, and the UK, which is not.

“As before, there are more questions than answers in this case, with the crime itself and who is behind it,” Maas said. The 18 Saudis were “allegedly connected to this crime”, Maas added, but he gave no further information. In Berlin, his office said it could not release the names because of German privacy protections.

The US has imposed sanctions on 17 Saudis alleged to have been involved in Khashoggi’s murder, but not the crown prince, Mohammed bin Salman, widely suspected of having ordered the assassination. The CIA is reported to have concluded that the prince was responsible, but Donald Trump has so far refused to endorse that finding.

Profile Who was Jamal Khashoggi? Show Jamal Khashoggi was one of the Arab world’s most prominent journalists and commentators. He was an outspoken critic of Saudi Arabia who dared to defy Crown Prince Mohammed bin Salman. While living in Saudi Arabia, Khashoggi was told to stop writing or posting on Twitter, where he had more than 1.6 million followers. He moved to the US in June 2017, where he continued to comment on his country both in print and on television. He wrote columns for the Washington Post and the Guardian.

His message struck a nuanced tone in the US, where he tried to acknowledge the reforms undertaken by Bin Salman while also highlighting the flaws. Khashoggi previously had close links with the Saudi royal family, including having served as a media aide to Prince Turki al-Faisal, when the latter was director general of the Saudi intelligence agency. He was also a former editor of the Saudi newspaper al-Watan and had worked with Prince Alwaleed bin Talal, a grandson of the first Saudi king. Khashoggi was murdered in the Saudi Arabian consulate in Istanbul in October 2018. Photograph: Virginia Mayo/AP

The US, UK and France have all insisted so far that their substantial arms sales to Riyadh will not be affected by the murder, undermining the impact of individual sanctions.

In his first public remarks since the killing on 2 October, Saudi Arabia’s King Salman praised the country’s judiciary, insisting his country would “never deviate” in its pursuit of justice, but he made no mention of the Khashoggi killing.

Khashoggi, a columnist for the Washington Post who had been critical of the Saudi royal family, disappeared after entering the Saudi consulate in Istanbul on 2 October. Riyadh offered contradictory explanations for his disappearance before saying Khashoggi was killed after “negotiations” to convince him to return to Saudi Arabia failed.

In an address to an advisory body on Monday – his first public comment since Khashoggi’s murder – King Salman made no direct mention of the crisis, though he lauded the country’s judiciary and public prosecutors for carrying out their duty in the service of justice.

US intelligence agencies have concluded that Salman’s son, Prince Mohammed, ordered the killing, which has put the Trump administration – close allies of the Saudis – in a difficult situation.

On Saturday Trump said his administration would “be having a very full report [on Khashoggi’s death] over the next two days, probably Monday or Tuesday”. He said the report would include “who did it”. It was unclear whether the report would be made public.

In an interview with Fox News broadcast on Sunday, Trump noted that Prince Mohammed had repeatedly denied being involved in the killing. “Will anybody really know?” Trump asked. “At the same time, we do have an ally, and I want to stick with an ally that in many ways has been very good.”

Roy Blunt, a Republican member of the Senate intelligence committee, said there was no “smoking gun” linking the crown prince to the killing. Blunt, who has received a confidential intelligence briefing on the matter, told ABC it was “hard to imagine” that the crown prince did not know about the killing, but he said: “I don’t know that we absolutely know that yet.”

He said Congress would await the Trump administration’s report in the next two days and the US would need to be clear about the ramifications of sanctions, given Saudi Arabia’s strategic role in the Middle East.