US President Donald Trump has called Saudi Arabia’s response to the murder of the dissident journalist Jamal Khashoggi “the worst cover-up ever”.

Those behind the killing in the Saudi consulate in Istanbul three weeks ago “should be in big trouble”, he said.

Shortly afterwards, Secretary of State Mike Pompeo said the US would “punish those responsible” and had revoked visas of 21 identified suspects.

The Saudi government has blamed the murder on rogue agents.

But President Erdogan of Turkey has said the journalist was the victim of a carefully planned “political murder” by Saudi intelligence officers and other officials.

Speaking to reporters at the White House on Tuesday, Mr Trump said: “They had a very bad original concept, it was carried out poorly and the cover-up was the worst in the history of cover-ups.”

“Whoever thought of that idea, I think is in big trouble. And they should be in big trouble.”

The Saudi government has provided conflicting accounts of what happened to Khashoggi, a US resident and Washington Post contributor. After weeks of maintaining he was still alive, senior officials now say the 59-year-old was murdered in a rogue operation after visiting the Saudi consulate in Turkey.

CIA director Gina Haspel has been sent to Turkey to review the matter. The pro-government Turkish newspaper Daily Sabah reports that Turkish intelligence officials have shared an audio recording from inside the Saudi consulate with her. Turkish media say the recording reveals gruesome details of the murder.

Trump’s public criticism of Saudi Arabia on Tuesday was his strongest so far, but he has continued to highlight the kingdom’s importance as a US ally.

In a separate interview with the Wall Street Journal, Mr Trump addressed the possible involvement of senior Saudi royals in the killing and said he did not believe King Salman had prior knowledge of the crime.

When asked about the possible role of Crown Prince Mohammed bin Salman, the president replied: “Well, the prince is running things over there more so at this stage. He’s running things and so if anybody were going to be, it would be him.”

He said he had questioned the crown prince about Khashoggi’s death, and been told he did not know about the operation when it was being planned.

Asked if he believed the royal family’s denial of any involvement in the killing, Mr Trump reportedly gave a long pause before saying: “I want to believe them, I really want to believe them.”