WASHINGTON: The United States has concluded that the weekend attack on Saudi oil facilities was launched from Iranian soil and cruise missiles were involved, a US official told AFP on Tuesday. The comments come as Secretary of State Mike Pompeo headed to the Kingdom Tuesday amid heightened tensions after the strikes. The official, who declined to be identified, said the United States was gathering evidence about the attack to present to the international community, notably European allies, at the UN General Assembly next week. Asked if Washington was certain that the missiles had been launched from Iranian soil, the official answered: "Yes." US intelligence services have the capability of determining where the missiles were launched from, the official said, declining, however, to say how many were fired. "I will not get into that kind of details," the official said. On Tuesday, Crown Prince Mohammed bin Salman spoke with UK prime minister Boris Johnson over the phone, with Johnson assuring the prince of the importance of a “collective global response” to the Aramco attack. The weekend strikes on Abqaiq -- the worlds largest oil processing facility – and the Khurais oil field in eastern Saudi Arabia have roiled global energy markets. Yemens Iran-backed-Houthi militants claimed responsibility for Saturdays attacks but Saudi Arabia accused Iran and President Donald Trump also singled out Tehran. "Certainly, it would look to most like it was Iran," Trump said Monday. The president said the United States wanted to help its Saudi ally but he wanted to avoid a war. US Vice President Mike Pence said on Tuesday the United States was evaluating evidence on the attacks on Saudi oil facilities and stands read to defend its interests and allies in the Middle East. If Iran conducted Saturdays attacks to pressure Trump to back off his sanctions regime against Tehran, they will fail, Pence said.  Tensions between Iran and the United States and its allies have threatened to boil over since May last year when Trump abandoned a 2015 nuclear deal and began reimposing sanctions in its campaign of "maximum pressure."