Britain has concluded that Iran was responsible for attacks on oil facilities in Saudi Arabia, UK Prime Minister Boris Johnson said Sunday.

He said the UK would consider taking part in a US-led military effort to bolster the Gulf kingdom’s defenses, while Iran’s president announced plans for a rival Iranian-led security coalition.

The UK Conservative prime minister also said the he would work with allies to “de-escalate” Middle East tensions that have soared since the September 14 attack on the world’s largest oil processor and an oil field. Britain had previously held back from attributing blame for the drone and missile attack.  Saudi Arabia and the United States say Iran was responsible, something Tehran denies.

Johnson told reporters flying with him late Sunday to New York for the UN General Assembly that now “the UK is attributing responsibility with a very high degree of probability to Iran” for the attack by drones and cruise missiles.

“We will be working with our American friends and our European friends to construct a response that tries to de-escalate tensions in the Gulf region,” Johnson said.

Shortly before leaving for the UN meetings Monday, Iranian President Hassan Rouhani said that his country will invite “all littoral states of the Persian Gulf” to join an Iranian-led coalition “to guarantee the region’s security.”

His remarks were broadcast on state television.

Rouhani said the plan — details of which he will present at the United Nations — is not limited to “security” but also encompasses economic cooperation and an initiative for “long-term” peace.

Iran’s president had already called on Western powers Sunday to leave the security of the Persian Gulf to regional nations led by Tehran.

Johnson said he would meet Rouhani at this week’s high-level UN gathering.

Johnson is also due to hold talks with US President Donald Trump, German Chancellor Angela Merkel and French President Emmanuel Macron.

He said he wanted Britain to be “a bridge between our European friends and the Americans when it comes to the crisis in the Gulf.”