An attack on Saudi Arabia that triggered the biggest jump in oil prices in almost 30 years was carried out with Iranian weapons, a Saudi-led coalition said on Monday, as U.S. President Donald Trump said Washington was "locked and loaded" to hit back.

Democratic Congresswoman and struggling 2020 presidential contender Tulsi Gabbard hit back at Trump's strong rhetoric. Gabbard wrote on Twitter in a reply to a Trump tweet, "Trump awaits instructions from his Saudi masters. Having our country act as Saudi Arabia's bitch is not 'America First.'"

The Iran-aligned Houthi group that controls Yemen's capital claimed responsibility for the attack, which knocked out more than half of Saudi Arabia's oil production and damaged the world's biggest crude processing plant.

Iran denied U.S. accusations it was to blame and said it was ready for "full-fledged war".

Read more: Washington may be ready for talks post-Bolton, but Iran is still hesitant | Analysis ■ Attack on Saudi oil infrastructure 'serious escalation' in proxy war with Iran | Explained

U.S. Ambassador to the United Nations Kelly Craft told the Security Council on Monday that emerging information on attacks on Saudi oil facilities "indicates that responsibility lies with Iran" and that there is no evidence the attack came from Yemen.

Britain's U.N. Ambassador Karen Pierce told the 15-council: "We're still assessing what happened and who's responsible for the attacks. Once this has been established we will discuss with our partners how to proceed in a responsible manner."

Two sources briefed on state oil company Saudi Aramco's operations told Reuters it might take months for Saudi oil production to return to normal. Earlier estimates had suggested it could take weeks.

A Saudi-led military alliance battling the Houthis said the attack on Saudi oil plants was done with Iranian weapons and was not launched from Yemen, according to preliminary findings.

Coalition spokesman Colonel Turki al-Malki said that an investigation into Saturday's strikes, which shut 5% of world crude output, was going on to determine the launch location.

"The preliminary results show that the weapons are Iranian and we are currently working to determine the location ... The terrorist attack did not originate from Yemen as the Houthi militia claimed," Malki told a press conference in Riyadh.