Washington (AP) - After drone strikes on the largest oil refinery in Saudi Arabia, US President Donald Trump has threatened to retaliate. At the same time Trump denied on Twitter his statement that he was ready without preconditions for a meeting with the Iranian leadership.

On Saturday, US Secretary of State Mike Pompeo blamed Iran for the attacks in Saudi Arabia, even though the Houthi rebels in neighboring Yemen had expressly pledged to do so. Tehran denied any involvement.

Trump made no statement as to who the US believes to be the originator of the attack. He wrote on Twitter: "There is reason to believe that we know the culprit." The US stood gun on foot, but waited for confirmation and information from the Saudi leadership who blamed it on the attack and under what conditions should be proceeded.

A few minutes later, Trump wrote in a Tweet that media reports that he was "unconditionally" prepared to meet the Iranian leadership were "as usual" wrong. Trump himself has repeatedly said that he is ready for such a meeting without preconditions. Only last Tuesday, Pompeo had again stressed that Trump was ready for a meeting without preconditions.

Pompeo wrote on Twitter on Saturday: "In the midst of calls for de-escalation, Iran has now launched an unprecedented attack on world energy supply. There is no evidence that the attacks came from Yemen. "

The influential US Senator and Trump confidante Lindsey Graham had said on Saturday to attack Iranian oil refineries. Such a move would "break the spine" of Tehran leadership, he wrote on Twitter.

Meanwhile, Trump approved the release of national oil reserves in the event of bottlenecks. Based on the attack "which could affect oil prices," he approved the release, if necessary, Trump wrote on Twitter. He has not yet determined the quantity, but it will be sufficient "to supply the markets well".

The drone strikes on the oil refinery in Saudi Arabia caused oil production in the kingdom to plummet dramatically. The production volume had plummeted by 5.7 million barrels per day, due to the "terrorist attacks", to about half of the usual volume per day, according to the Saudi state news agency SPA.

Early Saturday morning, several explosions had shaken assets of the state oil company Saudi Aramco in Churais and Abkaik. Videos on social networks saw big fires over the complexes. Experts see the drone attack as an attack on the center of the Saudi oil industry. According to Saudi Aramco, the complex is the largest refinery in the country and the largest crude oil stabilizer in the world.

A military spokesman for the Houthis had described the attack with ten drones as a "legitimate answer" to Saudi Arabia's ongoing military campaign in Yemen. The Arab kingdom is leading a US-backed military coalition in Yemen against the Houthis. These are in turn supported by Iran and keep large parts of the North Yemen including the capital Sanaa under control.

Trump tweet to Saudi Arabia

Trump tweet to Iran

Graham tweets