Gulf Arab states on Tuesday urged Syria's government to immediately halt its "killing machine", and called on arch rival Iran to stop interfering in their internal affairs.
The six-nation Gulf Cooperation Council also pledged to implement comprehensive reforms and strengthen economic and military integration as a first step towards forming a union.
In a statement issued at the end of their annual summit, held in Riyadh against the backdrop of the Arab uprisings, the GCC members called on Syria to "immediately halt its killing machine."
They appealed for Damascus to "put an end to bloodshed, lift all signs of armed conflict and release prisoners, as a first step towards implementing the (Arab) protocol".
Syria signed the accord with the Arab League on Monday after weeks of prevarication in the hope the 22-member bloc will lift sweeping sanctions against the regime.
"If there was goodwill when the protocol was signed, then these steps must be immediately taken," said Saudi Foreign Minister Prince Saud al-Faisal, adding the initiative was "proposed to prevent a civil war".
Despite the accord, at least 100 mutinous troops were killed or wounded on Tuesday, a day after up to 70 deserters were gunned down while trying to flee their posts, according to the Syrian Observatory for Human Rights.
More than 5,000 people have been killed in the Syrian regime's nine-month crackdown on dissent, the United Nations estimated on December 12.
In its concluding statement, the Gulf Cooperation Council also called on Iran to stop meddling in the internal affairs of the group's members.
"Stop these policies and practices... and stop interfering in the internal affairs" of Gulf nations, it said, expressing concern over Tehran's attempts to "instigate sectarian strife."
The Gulf states also called on their Shiite neighbour to "fully cooperate" with the International Atomic Energy Agency, adding GCC members were committed to a Middle East "free of weapons of mass destruction."
The West fears Iran's nuclear programme masks a push to develop an atomic weapons capability, a charge Tehran denies.
Saudi-Iranian relations have deteriorated since 1,000 Gulf troops entered Bahrain to help the Sunni monarchy crush Shiite-led democracy protests in February and March.
The ties worsened when US justice officials announced in October that they had foiled an Iranian plot to assassinate the Saudi ambassador to Washington.
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And tensions remain high even though the Iranian intelligence chief was in Riyadh last week to clear up misunderstandings over the alleged plot.
On Monday, the last of American troops withdrew from Shiite-dominated Iraq, further heightening Gulf fears over growing Iranian and Shiite influence in the region.
Hoping to ease tensions, the GCC urged Baghdad to step up its efforts to normalise ties with Kuwait, 10 years after the first Gulf war.
They called on Iraq to "implement its international commitments" towards its neighbour in a bid to "enhance trust between the two countries and strengthen their relations."
The two neighbours have not settled their border and Iraq still has to pay almost $20 billion in war damages resulting from the 1990 Iraqi invasion of Kuwait.
The Gulf states also expressed support for a Kuwaiti port project which Iraq says would strangle its shipping lanes in the narrow Khor Abdullah waterway, through which most of its oil exports enter the Gulf.
Kuwait insists the port will not affect Iraq.
The Gulf Arab nations, with the exception of Bahrain, for the most part evaded the turmoil of the Arab Spring.
In Saudi Arabia, however, Sunni-Shiite tensions have risen with several Shiite demonstrators from Eastern Province killed in anti-government protests.
Saudi Arabia, like Bahrain, accuses Iran of instigating the unrest among the Shiites in their country, and fear existing sectarian strife in Iraq could inflame existing tensions within their borders.
In response to the region's unprecedented upheaval, GCC chief Abdullatif al-Zayani said the group's six members agreed to "adopt Saudi King Abdullah's initiative to make the GCC countries a single entity".
On Monday, King Abdullah asked the GCC leadership to "move from a phase of cooperation to a phase of union," arguing the region's "security and stability are threatened" and that such challenges require "vigilance and a united stance."
The group also announced the establishment of a development fund worth about five billion dollars for Jordan and Morocco, though it did not clarify whether either nation would join the alliance of oil-rich monarchies.
Jordan and Morocco are the only Arab kingdoms not in the GCC, which comprises Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates, and has remained an exclusive club since its inception in 1981.
No practical measures have yet been taken to bring them into the group, despite a GCC proposal in May that they both join.