The brother of the Saudi King has made rare public criticism of the war in Yemen, blaming the monarch and powerful Crown Prince Mohammed bin Salman for the devastating conflict, which has killed thousands of civilians.

Prince Ahmed bin Abdulaziz al-Saud made the comments to a group of protesters outside his London home, The New Arab's Arabic-language service reported on Tuesday.

"What does the al-Saud family have to do with your chants? We have nothing to do with what is happening [in Yemen]. Certain officials are responsible... such as the king and the crown prince," Prince Ahmed tells protesters in a video posted online.

"I hope the war in Yemen ends after tomorrow," he added.

In another part of the video, the senior royal agrees with the protesters' condemnation of an August air strike in Yemen that killed dozens of civilians including 40 children.

He also expresses sympathy for detained Shia activists in Bahrain - a close Saudi ally - saying: "If we could [do something] we would, God willing".

The rare criticism from a member of the ruling al-Saud clan, hints at growing discontent over the aggressive policies of King Salman and his son, the crown prince.

Prince Ahmed is the younger brother of King Salman and a member of the so-called Sudairi Seven - a powerful bloc of sons of the kingdom's founder.

He served as the kingdom's deputy interior minister for 37 years, before briefly assuming the role of interior minister in 2012.

In 2015, a dissident prince called for the overthrow of King Salman and for the aging ruler to be replaced with Prince Ahmed.

The Saudi-led coalition intervened in Yemen in March 2015.

The devastating conflict has since left around 13,000 people dead and sparked what the UN has described as the world's worst humanitarian crisis.

The architect of the Yemen war, Crown Prince Mohammed bin Salman, has come under increasing scrutiny over his combative foreign policies.

The heir to the throne and de-facto ruler has led a year-long blockade of Qatar, cracked down on critics and potential rivals and has been accused of forcing the Lebanese Prime Minister Saad Hariri to resign while in Riyadh.