Gulf Arab leaders are expected to signal whether plans for monetary union by 2010 are feasible and raise concerns over growing Iranian influence in the region when they wrap up a summit meeting on Sunday.
Saudi Arabia's King Abdullah told Gulf Cooperation Council (GCC) leaders on Saturday they must set aside their differences to make European Union style economic integration a reality in the world's top oil exporting region.
Shortly before the king addressed the summit's opening, a Gulf official said Oman had informed the six-nation group that it could not join the monetary union in 2010.
King Abdullah also warned that the Middle East had become a "powder keg" waiting to explode because of conflicts in Iraq, Lebanon and the Palestinian territories.
"We still have much to do before we can say we have achieved complete economic union ... the obstacles are real but we should not lose sight of the dream," he said.
"Every country has had its reservations ... but united we will be a power that cannot be ignored."
The GCC groups Saudi Arabia, Qatar, Bahrain, Oman, Kuwait and the United Arab Emirates. Known for conservative political and economic policies, they maintain close alliances with the United States and share US concern over Iran.
The six have already agreed five criteria for economic union, including capping budget deficits at 3 percent of gross domestic product, public debt at 60 percent of GDP and inflation at the GCC average plus 2 percent.
Oman's central bank doubted the timetable for the single currency project last month and said others shared its concerns.
The Gulf official, who asked not to be named, told Reuters: "They (Oman) feel they are not going to be ready by 2010 ... Rather than delay the process, they want the other countries to move ahead, and they can join at a later date."
Bahrain Central Bank Governor Rasheed al-Maraj told Reuters on Sunday he believed the monetary plan was on track.
"I think we are moving according to the plan ... At the moment there is nothing official that has been said that we are going to delay," he said.
The summit is also discussing sectarian violence in Iraq, Iran's nuclear programme and rising tension in Lebanon.
King Abdullah said on Saturday that "dark clouds" were threatening civil strife in Lebanon, where opposition parties led by Shi'ite group Hezbollah are seeking to topple the Western- and Saudi-backed cabinet.