Prince Saud al-Faisal
Prince Saud al-FaisalUS State Department

Saudi Arabia on Thursday said it was 'weighing its response' to an Iranian plot to assassinate its ambassador in Washington, the Kingdom’s official SPA news agency reported.

"The kingdom, for its part, is considering decisive measures and steps it would take in this regard to stop these criminal actions..." SPA quoted security sources as saying of Iran's "outrageous assassination plot."

Saudi Foreign Minister Prince Saud Al Faisal took a more nuanced position, saying the kingdom would have a ‘measured response' after an event that has inflamed tensions between the Persian Gulf rivals.

"We hold them [Iran] accountable for any action they take against us," Prince Saud said in Vienna, where he was discussing opening a religious dialogue centre. "Any action they take against us will have a measured response from Saudi Arabia."

During his remarks al-Faisal said this was not the first time Iran had been suspected of similar acts, and condemned Tehran for trying to meddle in the affairs of Arab states.

Asked what actions Saudi Arabia might take, al-Faisal said: "We have to wait and see."

al-Faisal's remarks come after US officials announced Tuesday they had uncovered a plot by two Iranian men linked to Tehran's security agencies to hire a hit man to kill ambassador Adel Al Jubair with a bomb planted in a restaurant.

One man, Mansour Arbabsiar, was arrested last month, while the other is believed to be in Iran.

Iran has in the past assassinated its own dissidents abroad, but an attempt to kill an ambassador of another country would be a dramatic departure from previous patterns.

Iran has denied the charges and expressed outrage, saying the allegations threaten stability in the Gulf, where Saudi Arabia and Iran are fierce rivals.

US President Barack Obama spoke on Wednesday to Saudi King Abdullah about the plot, the White House said.

"The president and the king agreed that this plot represents a flagrant violation of fundamental international norms, ethics, and law," White House press secretary Jay Carney released in a statement.

Earlier Carney told reporters: "We're responding very concretely with actions we know will have an impact on Iran and will make clear this kind of behavior is unacceptable and will further isolate Iran."

Saudi Arabia and has repeatedly accused Iran of fomenting violence in Gulf Arab states, including its own Eastern Province, where the kingdom's Shiite minority is concentrated.