In a fit of diplomatic pique Saudi Arabia has spurned its chance to occupy a seat on the United Nations security council, accusing the world body of double standards and failing to do its duty over Syria, nuclear weapons and the Palestinians.

Months of simmering tension over the thorniest issues in the Middle East boiled over into public view on Friday in a strongly-worded complaint from Riyadh. Normal Saudi discretion was thrown to the winds in what appeared to be a concerted campaign to advertise its anger.

"Allowing the ruling regime in Syria to kill its people and burn them with chemical weapons in front of the entire world and without any deterrent or punishment is clear proof and evidence of the UN security council's inability to perform its duties and shoulder its responsibilities," said the Saudi foreign ministry. The issue was then amplified through a Twitter hashtag in Arabic.

Critics described it as a petulant and ineffective stunt that would undermine the conservative kingdom's ability to affect decisions it cares about.

Saudi Arabia is the leading supporter of armed Syrian rebel groups, some with an Islamist identity and agenda, seeking to overthrow President Bashar al-Assad. It is also a strategic opponent of Iran and alarmed by signs of a thaw in its relations with the US and the positive tone in this week's talks about its nuclear programme.

The statement came hours after Saudi Arabia was elected for the first time to the 10-strong rotating membership of the council, whose five permanent members are the US, Russia, China, France and Britain. Non-permanent members usually use their two-year stint to set the agenda and suppress international censure of their policies, especially on human rights. The general assembly holds a vote every year for five of the seats. The only precedent dates back to the depths of the cold war.

Signs of anger had been multiplying since last month when the Saudi foreign minister, Saud al-Faisal, refused to speak or even hand out a copy of his speech at the general assembly in anger over the security council deadlock on Syria and Palestine. That came shortly after the US-Russian agreement to disarm Syria's chemical weapons, which avoided the need for US-led air strikes and let Assad off the hook. "It was a sign of the frustration felt," said Nawaf Obaid, a senior adviser to Saudi officials.

The Saudi statement also complained that the UN had proved unable to resolve the Palestinian-Israeli conflict for decades and had failed to transform the Middle East into a zone free of weapons of mass destruction – presumably a reference to Israel's undeclared atomic arsenal and perhaps also to Iran's ambitions.

Frederic Wherey, a Saudi expert at the Carnegie Endowment, said: "This is a dramatic but ineffectual gesture. The Saudis realised the tide of the security council was against them on portfolios they care about. But operationally, it doesn't mean much. It's more theatrics than substance."

Chris Doyle of the Council for Arab-British Understanding said: "There is shock at their behaviour. The Saudis are the only member of the G20 who've never been on the security council. You have to question the sense of this. If they want to change the way the international community operates the UN is the perfect venue to make your voice heard. Do they expect the world to rush to Riyadh and apologise for not listening to them more? The whole thing seems petulant and very short term. It's a teenage tantrum."

After Thursday's vote the Saudi ambassador to the UN, Abdallah al-Mouallimi, said his country's election was "a reflection of a long-standing policy in support of moderation and in support of resolving disputes by peaceful means". But the statement from Riyadh appeared to take the envoy by surprise. "They worked hard to get in trained diplomats for the [UN] job," said Ali al-Ahmed, a US-based Saudi opposition commentator, "but maybe the king pulled the plug in one of his fits."

Edward Luck of the University of San Diego called the decision a "a baffling case of shooting oneself in the foot."

The Saudi move attracted as much ridicule and sarcasm as serious analysis. "Hopes for a UNSC resolution protecting the world's women from the dangers of driving shattered by Saudi decision to vacate its seat," tweeted the Middle East expert Marc Lynch. Analyst and wit Karl Sharro commented: "You would think Saudi Arabia would be more grateful that the UNSC allowed it to invade Bahrain and crush the uprising with no fuss."