The 57-member Organisation of Islamic Cooperation suspended Syria in a meeting attended by its staunch ally Iran, in a move hailed early Thursday by the United States as one that sends "a strong message" to Damascus.
A statement issued at the end of an OIC summit in the Saudi holy city of Mecca said participants had agreed on "the need to end immediately the acts of violence in Syria and to suspend that country from the OIC."
The final statement said there had been "deep concern at the massacres and inhuman acts suffered by the Syrian people."
OIC chief Ekmeleddin Ihsanoglu told a news conference the decision sent "a strong message from the Muslim world to the Syrian regime."
"This world can no longer accept a regime that massacres its people using planes, tanks and heavy artillery," he added.
It was "also a message to the international community stating that the Muslim world backs a peaceful solution (in Syria), wants an end to the bloodshed and refuses to let the problem degenerate into a religious conflict and spill over" into the wider region, Ihsanoglu said.
State Department spokeswoman Victoria Nuland said that "today's action underscores the Assad regime's increasing international isolation and the widespread support for the Syrian people and their struggle for a democratic state that represents their aspirations and respects their human rights,"
The OIC "sent a strong message to the Assad regime by suspending Syria's membership in the OIC," Nuland said from Washington.
"The United States commends the OIC for its action and commitment to a peaceful resolution in Syria."
The emergency summit of the world's largest Islamic bloc opened late Tuesday with the suspension proposal put forward by a preparatory meeting of foreign ministers, a symbolic attempt to pile pressure on Damascus over its deadly crackdown on a 17-month uprising.
The move by the OIC, which represents 1.5 billion Muslims worldwide, is aimed at further isolating Syrian President Bashar al-Assad's embattled regime, but its effect is seen as being largely symbolic.
Syria was suspended from the Arab League last year over its clampdown on the uprising that Assad characterised as a plot by Western and rival powers to overthrow his regime.
The meeting called for the "immediate implementation of the transitional peace plan and the development of a peaceful mechanism that would allow building a new Syrian state based on pluralism, democratic and civilian system."
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The participants also stressed "the principal responsibility of the Syrian government for the continuation of violence and bloodshed."
Algeria, Pakistan and Kazakhstan had called for the final statement of the summit, to which Damascus was not invited, to also pin blame on the armed opposition for the bloodshed in Syria, accor to informed sources at the summit.
And Egypt's President Mohamed Morsi proposed the formation of a committee grouping his country with key players Iran, Saudi Arabia and Turkey to try to find a settlement to the Syrian conflict, a delegate had said.
Saudi King Abdullah presided over the meeting, attended by Iranian President Mahmoud Ahmadinejad whose country has openly criticised the push to suspend Syria.
Iranian Foreign Minister Ali Akbar Salehi on Monday criticised the move to suspend Syria's membership of the OIC, saying it would not resolve the conflict and was not in line with the group's charter.
However, a source close to the participants told AFP that the Islamic Republic which had repeatedly voiced support to its Damascus ally met the decision with a "soft reaction."
Iran's president had avoided mention of the Syrian conflict in a 55-minute speech on Tuesday night as did Saudi Arabia's King Abdullah in his opening speech, indicating an accommodation between the region's superpowers who appeared on television footage to be chatting warmly during their meeting.
Tensions had been simmering for months between Sunni-dominated Saudi Arabia and Shiite-dominated Iran as Syria has emerged as another arena for the longtime rivalry between the two regional heavyweights.
"There has been a clear change in the Iranian position towards Syria," according to a diplomat at the Mecca summit.
In another conciliatory move, King Abdullah, whose country hosts the OIC headquarters in its Red Sea city of Jeddah, proposed Tuesday setting up a centre in Riyadh for dialogue between Muslim confessions.
Iran is the Syrian regime's biggest regional ally and has pledged its full support for Assad.
In a second statement called the "Mecca Pact," the participants proclaimed their support for "Muslim people who are oppressed like the Syrian people."
It underlined the summit's support for "the oppressed Muslim peoples... who face the combat aircraft and heavy guns of the regular armies as is the case of the Syrian people."
The statement backed cooperation between Muslim states, the fight against divisions between Muslims, promotion of "moderate" Islam and the "fight against terrorism and the thinking behind it."
It described as a "crime against humanity" the Myanmar government's handling of minority Muslims and reiterated support for the Palestinians.