Britain will be under increasing pressure to act against Saudi Arabia after the Gulf kingdom admitted dissident journalist Jamal Khashoggi was killed at its Istanbul consulate.

Saudi state television reported on Friday night that a primary investigation into the Washington Post columnist’s disappearance found he died after a fight broke out in the consulate in Turkey.

So far, 18 Saudi nationals have been arrested and deputy intelligence chief Ahmad al-Assiri and Saud al-Qahtani, a senior aide to Crown Prince Mohammed bin Salman, have been dismissed, state TV reported.

In the US, the White House said it acknowledged the latest announcement and reasserted its call “for justice that is timely, transparent and in accordance with all due process”.

The British Government is yet to publicly comment on the latest announcement, but the Press Association understands officials are considering the UK’s response to the reports.

Mohammed bin Salman visit to UK
Saudi Arabia’s crown prince Mohammad bin Salman is greeted by Prime Minister Theresa May at 10 Downing Street (Victoria Jones/PA)

Jeremy Hunt had earlier warned there will be “consequences” for the UK’s relationship with Saudi Arabia if it was found the journalist was murdered.

The Foreign Secretary said the Government remained “extremely concerned” about his fate after he went missing when he visited the consulate more than two weeks ago to get paperwork so he could marry.

White House press secretary Sarah Sanders said in a tweeted statement: “The United States acknowledges the announcement from the Kingdom of Saudi Arabia that its investigation into the fate of Jamal Khashoggi is progressing and that it has taken action against the suspects it has identified thus far.

“We will continue to closely follow the international investigations into this tragic incident and advocate for justice that is timely, transparent, and in accordance with all due process.

“We are saddened to hear confirmation of Mr Khashoggi’s death, and we offer our deepest condolences to his family, fiancée, and friends.”

Labour’s shadow foreign secretary, Emily Thornberry, has called for action to be taken, tweeting in response to the announcement late on Friday: “The Saudi lies and impunity must stop here.”

“We have heard the same excuses time and again from Saudi Arabia on Yemen, and now on Khashoggi: when disgraceful atrocities are committed, they call them unintended mistakes, and the world does nothing,” she said.

Earlier, former MI6 chief Sir John Sawers said “all the evidence” suggested that Mr Khashoggi had been murdered on the orders of someone close to the crown prince.

Turkish government sources have alleged Mr Khashoggi, a critic of the prince and the Saudi government, was tortured and murdered and by a hit squad flown in from Riyadh.

The Saudis first dismissed the claims as baseless, without providing an explanation as to how he disappeared after entering the consulate on October 2.

News of the arrests came as it was reported that members of the suspected hit squad came to Britain during the Saudi crown prince’s state visit in March, during which he met the Queen and Theresa May.

At least three of the suspects, First Lieutenant Dhaar Ghalib Dhaar Al-Harbi, Sergeant Major Walid Abdullah Al-Shihri and Abdul Aziz Muhammad Musa Al-Hawsawi, were part of the crown prince’s entourage, the news site Middle East Eye reported.

Another suspect, Major General Mahir Abdul Aziz Muhammad Mutrib, was seen emerging from a car in Downing Street during the visit, according to the Daily Mail.