"We are not at all happy with the situation," said Interior Minister Prince Naif. But he stressed that Riyadh was still ready to confront terrorism.

The traditionally close relationship between the US and Saudi Arabia has come under acute strain since the bombing began, with Saudi rulers fearing a serious public backlash if they appear to be supporting attacks on another Muslim country.

However, so far there is no threat to Saudi oil supplies, which could prove important if military action causes a sudden oil price rise.