US President Donald Trump has said that he is not satisfied with Saudi Arabia's explanation for the circumstances around the killing of journalist and government critic Jamal Khashoggi in Istanbul.

Speaking to reporters in Nevada, Mr Trump added that it was possible that Saudi Crown Prince Mohammed bin Salman had been unaware of the death.

Mr Trump had earlier said that he found Saudi Arabia's assertion that Mr Khashoggi died as a result of a fight credible.

"I do, I do," Mr Trump said when asked if the Saudis' explanation was credible, while adding: "It's early, we haven't finished our review or investigation."

The White House had earlier said it would press for justice after Saudi Arabia announced that Mr Khashoggi had died in the kingdom's consulate in Istanbul and that 18 Saudis had been arrested in connection with his death.

"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," White House spokeswoman Sarah Sanders said in a statement.

"We are saddened to hear confirmation of Mr Khashoggi's death, and we offer our deepest condolences to his family, fiancée, and friends," she added.        

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But members of Congress voiced scepticism about the Saudi public prosecutor's explanation that a fight broke out between Mr Khashoggi and people who met him when he went to the Saudi consulate in Istanbul on 2 October and that the altercation led to his death.

"To say that I am sceptical of the new Saudi narrative about Mr Khashoggi is an understatement," Republican US Senator Lindsey Graham, said on Twitter.

Mr Graham, who has been sharply critical of Saudi Arabia after Mr Khashoggi's disappearance, is a close ally of Mr Trump.

"First we were told Mr Khashoggi supposedly left the consulate and there was blanket denial of any Saudi involvement. Now, a fight breaks out and he's killed in the consulate, all without knowledge of Crown Prince," Mr Graham said.

"Its hard to find this latest 'explanation' as credible," he added.

Members of Congress have the power to block US arms sales to Saudi Arabia.

Mr Trump said last week he saw no reason to cut off weapons sales to Saudi Arabia in response to Mr Khashoggi's disappearance.

But, speaking prior to the Saudi announcements yesterday, Mr Trump said he might consider sanctions against Saudi Arabia over the journalist's disappearance, while emphasizing the importance of the US-Saudi relationship.

Democratic US Senator Richard Blumenthal told CNN the Saudi explanation "absolutely defies credibility" and he called for an international investigation of Mr Khashoggi's death.

"The Saudis very clearly seem to be buying time and buying cover. But this action raises more questions than it answers and there is no way the world will wait for 30 days for a Saudi investigation to be done," Mr Blumenthal said.

Democratic Senator Chris Van Hollen, called the Saudi statement a cover-up.