The six Gulf monarchies on Sunday criticised world inaction on Syria and Iranian "interference" in their internal affairs ahead of a visit to the Saudi capital by US Secretary of State John Kerry.
"The Syrian crisis has become more of a quasi-catastrophe through the unjustified killing of the Syrian people," Bahraini Foreign Minister Sheikh Khaled al-Khalifa said at the opening session of a Gulf Cooperation Council (GCC) meeting.
Sheikh Khaled criticised "the international community's lack of serious and rapid action" towards resolving the two-year conflict which the United Nations estimates has has cost more than 70,000 lives.
GCC members Saudi Arabia and Qatar have openly taken up the cause of the Syrian revolt and called for rebel forces to be armed in their battle against President Bashar al-Assad's regime.
The GCC nations also slammed what they charged was Iranian interference in their internal affairs.
Saudi Arabia, Bahrain, Qatar, the United Arab Emirates, Kuwait, and Oman "look forward towards better relations with Iran, but unfortunately the latter continues to interfere in their internal affairs," Sheikh Khaled said.
"It is important for our countries to stand united against such interference" from the Shiite Islamic republic across the Gulf, he said.
Relations between Iran and the GCC have plunged to a new low, with Tehran suspected of supporting Shiite opposition protests in Bahrain against the Sunni monarchy.
Tehran is also a staunch regional ally of Assad.
The GCC talks came with Kerry set to arrive in Riyadh later on Sunday, with Syria and Iran likely to top the agenda at his meetings.
Yemen, the GCC states' restive neighbour undergoing a difficult political transition, and the Saudi missile defence shield are also likely to be discussed, a diplomat said on condition of anonymity.
Kerry is also due to visit the United Arab Emirates and Qatar.