Saudi Arabia rejected membership of the UN Security Council on Friday, a day after it was elected to the body, accusing it of "double-standards" in resolving world conflicts.
"Work mechanisms and double-standards on the Security Council prevent it from carrying out its duties and assuming its responsibilities in keeping world peace," the foreign ministry said.
"Therefore Saudi Arabia... has no other option but to turn down Security Council membership until it is reformed and given the means to accomplish its duties and assume its responsiblities in preserving the world's peace and security," a statement said.
For the first time ever, oil-rich, conservative Saudi Arabia won a seat Thursday on the 15-member council, which has a key role in dealing with world conflicts.
Saudi UN Ambassador Abdullah al-Mouallimi said that reflected Riyadh's "long-standing policy in support of moderation and in support of resolving disputes in peaceful means."
But the foreign ministry said Saudi Arabia declines to be a member of a body unable to tackle long-standing conflicts in the Middle East or rid the region of the threat of nuclear war.
It pointed specifically to the nearly three-year civil war in Syria and the protracted Palestinian-Israeli conflict, as key reasons.
"Failing to find a solution to the Palestinian cause for 65 years" it said, has led to "numerous wars that have threatened world peace."
Likewise, it said, "allowing the regime in Syria to kill its own people with chemical weapons... without confronting it or imposing any deterrent sanctions... is a proof of the inability of the Security Council to carry out its duties and assume its responsibilities."
The ministry also criticised the body's "failure" to turn the Middle East into a region free from weapons of mass destruction, including nuclear arms -- in a reference to Iran and Israel.
Sunni-ruled Saudi Arabia is a fierce critic of Shiite Iran's nuclear programme, which the West and Israel suspect of seeking to develop a nuclear weapon, a charge Tehran denies. Israel is the sole, if undeclared, nuclear power in the region.
Saudi Arabia is a major backer of rebels trying to topple Syrian President Bashar al-Assad who is allied to Tehran.
Riyadh has been a vocal critic of the UN's handling of the conflict in Syria, where a peaceful movement that called for reforms emerged in March 2011 and was met with a brutal repression. It quickly escalated into civil war.
Last month, Saudi Foreign Minister Prince Saud al-Faisal refused to speak or even hand out a copy of his speech at the UN General Assembly in anger over the Security Council deadlock on Syria and Palestine.
"It was a sign of the frustration felt," said Nawaf Obaid, a visiting fellow at Harvard University's Belfer Center and an advisor to Saudi officials.
Five countries have permanent seats on the Security Council -- the United States, Britain, France, Russia and China. The other 10 seats are awarded for two-year periods by the General Assembly, which holds a vote every year for five of the seats.
Saudi Arabia was chosen by the 193-member UN General Assembly, along with Chile, Chad, Lithuania and Nigeria.
Security Council powers had cautiously welcomed Saudi Arabia's election.
"Having them on the Security Council allows you to debate those issues in a way which you can't if they are not on the council," said one UN diplomat.