Gulf Arab states demanded foreign militias quit Syria and said President Bashar al-Assad must have no future role Wednesday, in a declaration his Iran- and Hezbollah-backed regime denounced as meddling.
Wrapping up a two-day annual summit in Kuwait City, the Gulf Cooperation Council's leaders welcomed what they described as the new Iranian government's shift to a positive policy toward the six-nation bloc.
The GCC leaders also approved the formation of a joint military command, but postponed a decision on a proposed union.
Adopting a firm stance on Syria, the GCC "strongly condemned the continued genocide that Assad's regime is committing against the Syrian people using heavy and chemical weapons".
It called "for the withdrawal of all foreign forces from Syria," in a clear reference to Iran-backed Shiite militias from Iraq and Lebanon's Hezbollah movement which are supporting Assad's troops against Sunni-led rebels.
The GCC backed the opposition National Coalition's decision to attend a Geneva peace conference, saying the January 22 meeting should lead to the formation of a transitional government with extensive executive powers and in which Assad would have no role.
"Pillars of the Syrian regime whose hands had been stained by the blood of the Syrian people must have no role in the transitional government or Syria's political future," the oil-rich nations said in their summit's closing statement.
In response, Syria strongly condemned the "inflammatory rhetoric of the Council's statement on Syria, particularly as countries in the Council... support and practice terrorism".
"Those who participated today in the summit in Kuwait, first among them the Saudi regime, have contributed in large part to the killing of Syrians and the destruction of their country," said the foreign ministry.
"Their sorrow about the suffering of the Syrian people is nothing more than crocodile tears."
But brushing aside differences with Iran on Syria, the GCC praised the Islamic republic's overtures to Gulf Arab states.
The monarchies "welcome the new orientation by the Iranian leadership towards the Gulf Cooperation Council and hope it will be followed by concrete measures that would positively impact regional peace," said the statement.
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They also "welcome the interim deal signed by the P5+1 and Iran as a first step toward an inclusive and lasting agreement on Iran's nuclear programme that would end international and regional concerns."
While welcoming the nuclear deal, Kuwait's Foreign Minister Sheikh Sabah Khaled Al-Sabah told reporters the Gulf states would "monitor the issue closely and through direct consultations with our allies."
The GCC members, he added, had not requested to take part in negotiations for a final agreement on Iran's nuclear programme.
Iran's Foreign Minister Mohammad Javad Zarif toured the Gulf last week to assure some of its governments the nuclear deal was not at their expense, while calling for a new page in relations.
Like Western powers, Gulf monarchies fear Iran wants to develop atomic weapons under the guise of a civilian nuclear programme. Iran says the programme is for peaceful purposes only.
Ties between some Gulf states and Iran have also been strained over Tehran's support for Assad and a Shiite-led uprising in Bahrain.
This year's summit was also held amid differences over a Saudi proposal to upgrade the GCC into a confederation.
At the weekend, Oman -- which reportedly hosted secret talks that led to the Iranian nuclear deal -- threatened to pull out of the loose alliance if a union was announced, while Saudi Arabia, which is solidly backed by Bahrain, has insisted it is time to move ahead.
Wednesday's final statement said Gulf leaders had directed the ministerial council to continue consultations on the matter.
Sheikh Sabah told reporters that "consultations will continue until we reach consensus".
However, the Gulf Arab leaders approved the creation of a unified military command "as part of efforts aimed at strengthening security and stability".
No details were provided on the structure or duties of this command.
The GCC states -- Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates -- formed the Peninsula Shield force in 1982 as a 5,000-strong force but has since expanded to more than 30,000 troops.
Together, the six states sit on 40 precent of global crude reserves and a quarter of the world's natural gas. They have a population of 47 million, about half of them foreigners.