Prime Minister Theresa May is under pressure to suspend arms sales to Saudi Arabia after the Gulf kingdom admitted that 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.

The explanation about Khashoggi's death was met with widespread scepticism yesterday, and the Prime Minister has been urged to stop selling arms to the kingdom.

Saudi Arabia is the UK's key ally in the region and also a significant trading partner. Britain rolled out the red carpet for Crown Prince Mohammed bin Salman in March.

During his state visit he was granted rare access to a briefing on foreign policy issues by national security officials alongside his meetings with the Queen and Prime Minister.

Foreign Secretary Jeremy Hunt is considering the "next steps" in Britain's response to the case, officials said.

Hunt previously warned there will be "consequences" for the UK's relationship with Saudi Arabia if it was found the journalist was murdered.

Shadow international trade secretary Barry Gardiner told BBC Radio 4 yesterday: "What we would do certainly at the moment, and I think the Government should do this, is to suspend all arms sales to the kingdom."

Gardiner acknowledged there were a "lot of jobs" in the UK linked to the defence trade but said "this is about who we are as a country".

Liberal Democrat leader Sir Vince Cable said the case gets "murkier and murkier". He added: "The Government should have already suspended arms export licences to Saudi Arabia…this reinforces the argument for loosening the bonds to the regime."

The Prime Minister yesterday refused to answer questions about the fate of Khashoggi and whether or not the UK would suspend arms sales to the Gulf state now it has confirmed Khashoggi is dead.

A number of Saudi nationals have been arrested and deputy intelligence chief Ahmad al-Assiri and Saud al-Qahtani, a senior aide to the Crown Prince, have been dismissed, state TV reported.

US President Donald Trump said Saudi Arabia's announcement that suspects are in custody over the journalist’s death was a "very important first step". Trump said he would work with Congress on a US response.

The president was speaking at a defence roundtable event in Arizona hours after Saudi Arabia claimed that Khashoggi, who was last seen on October 2, was killed in a "fistfight" at the Saudi consulate in Istanbul.

Asked by a reporter whether he thought Saudi Arabia's explanation for Khashoggi's death was credible, Trump said "I do. I do."

Democratic Representative Adam Schiff of California said Saudi Arabia's claim that Khashoggi died in a brawl was not credible.

"If Khashoggi was fighting inside the Saudi consulate in Istanbul, he was fighting for his life with people sent to capture or kill him," said Schiff, the ranking member of the House Intelligence Committee.

"The kingdom and all involved in this brutal murder must be held accountable, and if the Trump Administration will not take the lead, Congress must," he said.

Senator Tim Kaine, the 2016 Democratic vice presidential nominee, added: "The Saudi 'explanation' for murdering journalist and Virginia resident Jamal Khashoggi in a consulate - a fistfight gone wrong - is insulting...since the Trump administration won't stand up against atrocity, Congress must."

Trump said yesterday he wanted to talk to Saudi Crown Prince Mohammed bin Salman before deciding what to do next.

"Saudi Arabia has been a great ally, but what happened is unacceptable," the president said.

Of the Saudi arrests, he added: "It's a big first step. It's only a first step, but it's a big first step."

Turkish government sources have alleged that Khashoggi, a critic of the prince and the Saudi government, was tortured and murdered 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 to obtain paperwork for his forthcoming marriage.

Members of the suspected hit squad reportedly came to Britain during the prince's state visit.

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 reportedly part of his entourage.

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

A UK Foreign Office spokesman said: "We send our condolences to Jamal Khashoggi's family after this confirmation of his death.

"We are considering the Saudi report and our next steps.

"As the Foreign Secretary has said, this was a terrible act and those responsible must be held to account."