US Secretary of State Mike Pompeo is in Saudi Arabia on the latest leg of his regional tour, with the murder of journalist Jamal Khashoggi and the blockade of neighbouring Qatar high on the agenda.

Early on Monday, the top US diplomat arrived in the Saudi capital, Riyadh, where he will meet King Salman bin Abdul Aziz, after meeting Qatari officials a day earlier in Doha.

During that visit, Pompeo called for an end to the 19-month blockade of Qatar by a quartet of Arab countries, including Saudi Arabia, Bahrain, Egypt, and the UAE.

The bloc accuses Qatar of supporting groups it has proscribed as "terrorist groups", a charge Doha vehemently denies.

"We are all more powerful when we are working together and disputes are limited," Pompeo said at a joint news conference with Qatari Foreign Minister Mohammed bin Abdulrahman bin Jassim Al Thani on Sunday.

Attempts at mediation between Qatar and the blockading nations have stalled, as highlighted by the recent resignation of US envoy Anthony Zinni - who quit because of an apparent "lack of will" on behalf of "regional leaders" for regional reconciliation.

Khashoggi murder

Also high on the agenda is the murder of Saudi journalist Khashoggi at the Saudi consulate in Istanbul in October last year. The Washington Post columnist's slaying by a Saudi hit squad prompted international outrage, especially among US media outlets and politicians.

Western intelligence agencies, including the CIA, have strongly hinted that the killing could not have taken place without the authorisation of Saudi Crown Prince Mohammed bin Salman.

US politicians have called for tough action against the prince, but President Donald Trump and Pompeo have so far been reluctant to directly implicate the royal or issue any punitive measures.

Instead, Pompeo has called on the Saudis to ensure Khashoggi's killers are held accountable, avoiding any suggestion that Prince Mohammed was involved.

It is not clear whether Pompeo will meet Prince Mohammed in Riyadh on Monday.

Long seen as a royal family insider, Khashoggi found himself on the wrong side of the crown prince for publicly criticising some of his policies.

Pompeo is due to visit Oman next but will cut short his tour and miss a scheduled visit in Kuwait due to a death in his family, the US State Department said, adding he would visit the country "at an agreeable time".

His tour comes amid conflicts raging in Syria and Yemen, while the US is trying to ensure a unified front against Iran, which it accuses of expanding its political and military footprint in the Middle East.