RIYADH (Reuters) - Saudi Arabia said on Monday that the attack on its oil facilities was carried out with Iranian weapons, according to a preliminary investigation, but stopped short of directly blaming regional foe Iran.

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A foreign ministry statement said Riyadh would invite international experts, including from the United Nations, to participate in investigating Saturday’s assault, which cut almost half of Saudi Arabia’s oil production.

The United States, which has blamed Iran for the strikes, is studying all available options in addressing the assault, U.S. Defense Secretary Mark Esper told Saudi Crown Prince Mohammed bin Salman in a phone call on Monday, Saudi state media said.

“Initial investigations show that Iranian weapons were used in the attacks and work is going on to determine the source of those attacks,” the foreign ministry statement said.

“The kingdom is capable of defending its land and people and responding forcefully to those attacks,” it added.

Yemen’s Iran-aligned Houthi movement has claimed responsibility for the strikes, but the spokesman for the Saudi-led military coalition battling the group said preliminary findings indicated the attack was not launched from Yemen.

Tehran has dismissed the U.S. accusations as “unacceptable” and said it was ready for a “full-fledged war.”

Riyadh called on the world to condemn those behind the attack on the world’s top oil exporter, a key regional U.S. ally which has supported U.S. President Donald Trump’s “maximum-pressure” campaign on Shi’ite Muslim Iran.

Prince Mohammed, Saudi Arabia’s de facto ruler, told Esper that Iranian threats “are not only directed to the kingdom, but affect the Middle East and the world,” news agency SPA said.

Pakistan Prime Minister Imran Khan, who also called the crown prince on Monday, offered his country’s “full support and capabilities” to the Gulf Arab state, it added.

The Wall Street Journal reported that U.S. officials had said intelligence indicated Iran was the “staging ground” for the attack and had shared the information with Riyadh. It quoted people familiar with the discussions.

Coalition spokesman Colonel Turki al-Malki told reporters in Riyadh earlier on Monday that authorities were still determining the launch location.

“The terrorist attack did not originate from Yemen as the Houthi militia claimed,” he said, adding that authorities would reveal the location from where drones were launched at a future news conference.

The Saudi-led coalition of Sunni Muslim countries intervened in Yemen in March 2015 against the Houthis, who ousted the internationally recognized government from power in the capital Sanaa, to prevent Iran from gaining influence through the group.

The movement, which denies being a puppet of Tehran and says it is fighting a corrupt system, recently stepped up drone and missile attacks on Saudi cities. The conflict is largely seen in the region as a proxy war between Saudi Arabia and Iran.