Saudi Arabia on Sunday warned against threats to punish it over last week’s disappearance of journalist Jamal Khashoggi, as European and US allies piled on pressure.

US President Donald Trump has threatened “severe punishment” if it turns out Khashoggi was killed inside the Saudi consulate in Istanbul, though he said Washington would be “punishing” itself if it halted military sales to Riyadh.

“The Kingdom affirms its total rejection of any threats and attempts to undermine it, whether by threatening to impose economic sanctions, using political pressures, or repeating false accusations,” the official Saudi Press Agency quoted an unnamed official as saying.

“The Kingdom also affirms that if it receives any action, it will respond with greater action, and that the Kingdom’s economy has an influential and vital role in the global economy,” the official added, without elaborating.

Europe’s largest economies — Britain, France and Germany — said on Sunday they were treating the case with “the utmost seriousness”.

“There needs to be a credible investigation to establish the truth about what happened, and — if relevant — to identify those bearing responsibility for the disappearance of Jamal Khashoggi, and ensure that they are held to account,” the countries said in a joint statement.

“We encourage joint Saudi-Turkish efforts in that regard, and expect the Saudi government to provide a complete and detailed response. We have conveyed this message directly to the Saudi authorities.”

US senators called for reactions ranging from boycotting an upcoming economic summit in Riyadh to ending support for Saudi military operations in Yemen.

“If they lured this man into that consulate, they went medieval on him, and he was killed and he was chopped up and they sent a death crew down there to kill him and do all of this, that would be an outrage,” Florida Senator Marco Rubio told CNN’s State of the Union.

The Saudi stock market fell as much as 7 per cent in early trade on Sunday, one of the first signs of economic pain Riyadh could suffer over the affair. By close, it had recovered some losses, ending down 3.5 per cent and losing $16.5 billion of market value.

The crisis has polarised Saudis, with some blaming the nation’s enemies and others concerned about the direction the country is heading under Prince Mohammed.

Saudi Gulf affairs minister Thamer al-Sabhan said there had been a “frenzied campaign” to spread lies over the affair and that it was “known” who was behind that, wording used in the past to refer to Qatar and the Muslim Brotherhood.

Abdulrahman bin Abdullah al-Sanad, head of the body overseeing the Saudi religious police, called for unity. “Defending the Kingdom of Saudi Arabia and standing for it and its leaders is a religious duty and a national demand,” he tweeted.

A Turkish official told Reuters on Sunday that the Saudis had said they would allow the consulate to be searched, and that this would happen by the end of the weekend, though he conceded to “flexibility on this date”.