Turkey, Saudi Arabia and Pakistan held the first meeting on Monday of a committee formed as part of a defence pact at Istanbul.
The 'Mecca Joint Defence Agreement', signed on August 7, brought together Sunni Muslim US allies concerned by the Iran war and regional conflict that has led to Iranian missile fire on Gulf oil exporters.
It is intended to strengthen collective deterrence against any act of aggression and stipulates that an armed attack against any of the three would be regarded as an attack on all, similar to NATO's Article 5 collective defence clause.
Foreign and defence ministers of the three countries, as well as senior military officials gathered for a family photo ahead of the meeting in Istanbul's Ciragan Palace.
Foreign and defence ministers, as well as the chiefs of staff, of the three countries will attend the meeting in Istanbul, a Turkish foreign ministry source said.
"International security issues will be on the agenda," the source said, with discussions expected to cover enhancing defence capabilities, greater interoperability among their armed forces and deepening cooperation in the defence industry, including joint production and development.