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Pakistan, Saudi Arabia and Turkiye agreed to rapidly deploy military forces and capabilities after an emergency meeting in Riyadh.
The decision was announced in a joint statement from Pakistan's foreign ministry.
The Mecca Alliance said it would activate collective deterrence measures in response to attacks on Saudi Arabia and holy sites.
The announcement followed condemnation of recent attacks by Yemen's Houthi group.
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Reports also said Saudi-backed forces launched a major offensive against the Houthis in Yemen.
One report said retired Lieutenant General Nauman Mahmood was appointed as the alliance's first Secretary-General.