Saudis swore allegiance on Saturday to new Crown Prince Nayef bin Abdul Aziz, described by the local press as the "man for the job" and praised in Washington for his commitment to fight terrorism.

Nayef, who served as interior minister for nearly four decades and led a crackdown on Al-Qaeda in the kingdom, was named in a royal decree on Thursday to succeed Prince Sultan who died in the US last week following a long illness and was buried in Riyadh.

In his first statement after his promotion, Crown Prince Nayef thanked the monarch for his "trust," saying in remarks aired Saturday on state television that he "appreciates the responsibility" of the new post.

Nayef also praised King Abdullah for his leadership during a troubled time in the Arab world, with protests that have largely spared the kingdom sweeping several countries, unseating three presidents so far.

"He has succeeded in making the kingdom peaceful and stable... thanks to his wise leadership. Otherwise, we would have been hit like others. But thanks to Allah, we have a good and capable king, and a decent people," he added.

The new crown prince received his subjects in a royal palace in Riyadh, according to state media.

The ceremony was open to all citizens, who poured in to greet him in keeping with the tradition in the absolute monarchy.

Citizens in other regions in the vast desert kingdom will be able to pledge allegiance on Sunday to provincial governors, all of whom are members of the Al-Saud royal family.

Thursday's appointment of Prince Nayef, 78, as crown prince, "was a source of satisfaction for all Saudis," Al-Watan daily said, praising him as having the qualities of a "man of state."

He "well deserved the position given his security and political experience," said Al-Riyadh daily of Nayef, who was promoted from second vice prime minister to first deputy. Nayef has also headed the ministry of interior for 36 years.

"He is the man for the job," because internal and regional dynamics "require an experienced and determined man" in power, said Al-Jazeera, another Saudi paper, in an editorial under the title "the man for difficult missions."

US President Barack Obama welcomed the choice of Nayef as a successor to the throne of the oil-rich kingdom, a major US ally in the Middle East.

"We in the United States know and respect him for his strong commitment to combating terrorism and supporting regional peace and security," Obama said in a statement on Friday.

Reputed for being an iron-fisted man, Nayef has become a bastion of the Al-Saud dynasty, overseeing a highly-successful fight against Al-Qaeda, but also dealing swiftly and sternly with all forms of opposition.

Under his leadership, the interior ministry faced the rise of Al-Qaeda in the kingdom with a bloody wave of attacks between 2003 and 2006.

He cracked down on the network, forcing its leaders and its members to flee to Yemen where they continue to threaten Saudi interests. He also dismantled charitable organisations that collected donations for the network.

Nayef also oversees security measures during the annual Muslim hajj pilgrimage to Mecca, which attracts around two million people from abroad, and whose rites for the year begin next week.

Liberals and rights activists appear worried by the further strengthening of the powers of Nayef, who is known for being close to the conservatives.

A petition signed by 91 activists Saturday urged him to "release thousands of political prisoners" and to lift an "unrightful" ban on travel imposed on some activists.

"Perhaps the first thing to do in your new post is to end the suffering of the families of the prisoners and bring them together to make them happy and end their misery," the petition said.

Meanwhile, the king has not named a new defence minister to replace Sultan who held the portfolio since 1962, raising questions over disputes within the royal family.