Saudi Arabia, Turkey and Pakistan signed a joint defence pact in Mecca today.
The agreement aims to "strengthen collective defence" and "stipulates that any armed attack against any one of the three states shall be regarded as an attack against them all", according to a joint statement.
The deal follows a period of heightened instability in the Middle East centred around the US-Iran war.
Saudi territory, including its oil and gas assets, has been repeatedly attacked by Iran and Iran-backed groups in Iraq and Yemen since the start of the war. It remains unclear what the defence pact commits the three states to in the event of any attack.
Turkey was also targeted in the war's early stages.
The agreement aligns three Sunni-majority Muslim countries closer together, with each bringing different strengths.
Saudi Arabia is Opec's leading member and one of the world's largest oil producers, giving it significant financial power. Turkey has Nato's second largest army and has developed a strong defence industry in recent years, while Pakistan is the world's fifth most populous country and has nuclear weapons.
Some analysts see the emerging alliance as a reaction to destabilising moves in the region by the US and Israel on the one hand and Iran and its proxies on the other.
It follows an earlier defence pact signed between Saudi Arabia and Pakistan in September.
