Al-Qaeda is actively seeking to bring down the Saudi ruling royal family, the US Deputy Secretary of State, Richard Armitage, has said.
Armitage held talks with Crown Prince Abdullah
Osama Bin Laden's organisation has long been a critic of the Saudi Government, regarding it as too pro-American.
Mr Armitage also warned of fresh terror attacks to come in the kingdom.
He was speaking after holding talks in Saudi Arabia with Crown Prince Abdullah following Saturday's suicide bombing in Riyadh, which killed at least 17.
The target was a foreign workers' residential compound close to the homes of several Saudi ministers.
More than 120 people were injured, most of them non-Saudi Arab workers and their families.
The BBC's Paul Wood, from the scene of the blasts, says the bombers penetrated far into the compound before detonating their explosives.
Buildings of several storeys high were reduced to rubble, he adds.
Mr Armitage, who arrived in Riyadh on Sunday, told reporters: "I can't say that last
night's attack was the only or the last attack.
"My view is these al Qaeda terrorists - and I believe it was al Qaeda - would prefer to have many such events."
And in an interview with the Dubai-based al-Arabiya television channel, he said: "It's quite clear to me that al-Qaeda wants to take down the royal family and the Government of Saudi Arabia."
In a BBC interview, the Saudi ambassador to London, Prince Turki al-Faisal, a former intelligence chief in Riyadh, openly admitted that it would be impossible to prevent such attacks from recurring.
Hundreds of people have been arrested by the Saudi authorities over the past six months.
Some clerics have begun mediation efforts to try to open talks between the militants and the government.
The effort is led by Dr Mohsen al-Awaji, spokesman for an organisation called the Global Anti-Aggression Campaign.
There is anger in Riyadh over the attack on the compound, which killed mainly Arabs and occurred during the holy month of Ramadan.
Saudi officials said seven Lebanese, four Egyptians, one Saudi, one Sudanese and four unidentified people had been killed. The dead included five children.
Our correspondent says such an attack is likely to alienate potential supporters of the militants.
The Saudi ambassador to London told Reuters news agency that the bombing of a Arab housing compound showed that the militants were aiming at soft targets.
VIOLENT WEEK IN THE KINGDOM
3 Nov: Police kill two 'militants' in Mecca, capture six
6 Nov: Two al-Qaeda suspects blow themselves up in Mecca in shoot-out with police
6 Nov: Riyadh police shoot dead third suspect from Mecca
8 Nov: US diplomatic missions closed amid "terrorist threat"
9 Nov: Compound attacked
"It is a clear sign of a desperate group that wants to show it can do things... Hence they chose the target that they did," said Prince Turki al-Faisal.
"They want to show they can do something, after all the successes that we've had in tracking down these people over the last six months."
Saudi officials have said the attack was similar to the attack on a Western compound in Riyadh in May which left dozens dead.
Saudi Interior Minister Prince Nayef Bin Abdul Aziz said the authorities would track down the perpetrators of the crime "who claim to be Muslim".
The US has put pressure on Saudi Arabia to act against al-Qaeda since the 11 September attacks on New York and Washington which were carried out mainly by Saudi nations.
The US, which had closed its diplomatic missions in Saudi Arabia on Saturday because of a heightened threat of attack, ordered its diplomatic staff and their families in the country to remain at home.
Embassy officials said the missions would remain close until at least Tuesday.