The crisis-hit Gulf Cooperation Council summit was going ahead in Kuwait City but amid uncertainty over which leaders from among Riyadh and its allies would join their Qatari rival for the talks.
The future of the six-nation GCC -- formed 36 years ago to bring together energy-rich Sunni Arab Gulf states -- appeared to be hanging in the balance.
This year's meeting comes with Saudi Arabia and its allies engaged in a bitter dispute with fellow GCC member Qatar, in the worst crisis ever to hit the bloc.
Qatari Emir Sheikh Tamim bin Hamad Al-Thani accepted an invitation to attend, but with only hours before talks were due to begin, Saudi King Salman sent his foreign minister, Adel al-Jubeir, in his stead.
Bahrain sent its deputy prime minister and Emirati media said the state minister for foreign affairs would represent Abu Dhabi.
Those three Gulf states, together with Egypt, cut all ties with Qatar on June 5, accusing the gas-rich emirate of supporting Islamist extremists and of being too close to Shiite Iran, Riyadh's arch-rival.
Qatar denies the allegations and has accused the Saudi- led bloc of aiming to incite a change of regime in Doha.
Kuwait has been leading mediation efforts within the GCC to resolve the crisis, but so far with little success.
Casting further doubt on the group's future, the UAE said Tuesday it was forming a new military and economic committee with Saudi Arabia separate from the GCC.
The committee "will coordinate between the two countries in all military, political, economic, trade and cultural fields," according to a decree issued by UAE President Sheikh Khalifa bin Zayed Al-Nahyan.
Founded in 1981, the GCC is a political and economic union grouping Qatar with Bahrain, Saudi Arabia and the United Arab Emirates as well as Oman and Kuwait.
Dominated by Riyadh, it has been a regional counterweight to Iran, Sunni Saudi Arabia's Shiite rival across the Gulf.
On Monday, the foreign ministers of Saudi Arabia and Qatar attended round-table talks ahead of the gathering, in their first such encounter since the diplomatic crisis erupted in June.
Omani Minister of State for Foreign Affairs Yussef bin Alawi sat between them at the meeting which the foreign ministers of the UAE, Bahrain and Kuwait also attended.
After cutting off all ties with Qatar, Saudi Arabia and its allies imposed a land, sea and air blockade of the emirate and issued a list of 13 demands to have it lifted.
Bahrain in October called for Qatar's membership of the GCC to be suspended until it accepted the demands.
Experts warn that the crisis could lead to the demise of the once-powerful GCC.
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