Britain believes Iran was responsible for an attack on Saudi oil facilities and will work with the United States and European allies in a joint response, Prime Minister Boris Johnson said Monday.
The United States and Saudi Arabia have already blamed Iran for the September 14 attacks that initially cut Saudi oil production by half.
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The Yemeni Houthi movement, aligned with Iran, has claimed responsibility.
"The United Kingdom attributes responsibility with a very high degree of probability to Iran for the Aramco attacks. We believe that Iran is very likely to be really responsible," Johnson told reporters on the plane to the United Nations General Assembly in NY.
"We will work with our American friends and our European friends to build a response that attempts to reduce tensions in the Gulf region."
A UK government official said the Houthi claim of responsibility was "unlikely", since the scale, sophistication and scope of the attack were inconsistent with their capabilities.
"It is unlikely that he would not have been authorized by the Iranian government," the official said.
When asked if Britain would rule out military action, Johnson said he would be closely watching a US proposal to do more to help defend Saudi Arabia.
"Clearly, if the Saudis or the Americans ask us to play a role, we will consider how we could be useful," he said.
Johnson said he would be discussing Iran's actions in the region with President Hassan Rouhani at the UN meeting, and would press for the release of several Iranians with dual citizenship who, he said, were being held "illegally and unfairly."