US Secretary of State Mike Pompeo has arrived in Saudi Arabia's capital, Riyadh, for high-level discussions with the kingdom's leaders.

During his visit, which started on Wednesday - the first since the US forces killed a top military commander of Saudi Arabia's regional rival Iran, leading to soaring tensions - Washington's top diplomat will hold discussions with King Salman and his son Crown Prince Mohammed bin Salman (MBS), the kingdom's de facto ruler.

Pompeo is expected to remain in the kingdom until Friday, before departing to neighbouring Oman, a close US ally that maintains ties with both Saudi Arabia and Iran.

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Before his arrival in Riyadh, Pompeo said he planned to raise US concerns over Saudi Arabia's human rights record, including the case of a Saudi-American doctor who is facing trial and barred from leaving the kingdom and allegedly tortured.

When asked by a reporter whether he would specifically raise the case of Walid Fitaihi, Pompeo said: "I'm sure I'll bring up that issue and a wide range of human rights issues, as well."

He added: "In each of the visits I've had to the kingdom during my time both as CIA director and as secretary of state, we raised these important issues, these issues that matter a lot to the American people."

Allegations of torture

A day before Pompeo was scheduled to arrive in Saudi Arabia, the two lead congressmen in the House Foreign Affairs Committee wrote to him to urge him to raise the case of Fitaihi with Saudi government officials.

Fitaihi, a Boston-area physician, was detained in Saudi Arabia in November 2017 during an unprecedented anti-corruption crackdown initiated by MBS, which targeted senior princes, ministers and businessmen.

At the time, some 200 people were detained in Riyadh's Ritz-Carlton hotel for weeks, and even months. They were forced to sign over billions of dollars in assets to the government during the shakedown which helped the young crown prince consolidate power.

Fitaihi was released from detention last year, but he and seven members of his family, all of whom are US citizens, have been barred from leaving Saudi Arabia while he stands trial, the congressmen said. It is unclear what specific charges Fitaihi faces.

Democratic Representative Eliot Engel of New York and Republican Representative Michael McCaul of Texas said in their letter that Fitaihi was held without charge for almost two years.

Ahmed Fitaihi has told members of Congress that his father was beaten, electrocuted and subjected to other forms of torture and allowed little contact with his family during his detention. Fitaihi returned to his native Saudi Arabia in 2006, where he helped found a hospital built by his family and became a popular motivational speaker on television.

Activists arrested, Khashoggi murdered

Since becoming crown prince in June 2017, MBS has touted economic and social openness in the traditionally closed-off country. At the same time, however, authorities have continued rounding up critics, an effort that gathered pace in September 2017 with the arrests of prominent religious leaders, some of whom could now face the death penalty.

In mid-2018, just as Riyadh lifted a ban on female motorists, more than a dozen women's rights activists were arrested including some campaigning for the right to drive. Local media tarred them as traitors, and a court has charged some of them with crimes including contacts with foreign journalists.

In a report released in November last year, Human Rights Watch said critics of the kingdom are still being vigorously pursued with measures including arbitrary travel bans and harassment of their families. These include prominent Muslim scholars, women rights activists and members of the royal family.

The prince's reputation was further tarnished internationally after the 2018 murder of Washington Post journalist Jamal Khashoggi, a critic of MBS, inside the Saudi consulate in Istanbul.

To date, public protests, political parties and labour unions are banned in Saudi Arabia, where the media are controlled and criticism of the royal family can lead to prison.