UN Secretary-General Ban Ki-moon says he has received no notification from Saudi Arabia that it will turn down a seat on the UN Security Council.
Earlier the Saudi foreign ministry said it had turned down the non-permanent seat, accusing the world body of "double standards".
The ministry said the UN needs to be reformed first.
It said the Security Council had failed in its duties towards Syria as well as in other world conflicts.
Mr Ban refused to say whether he would be speaking to the Saudi king about the matter.
"I understand that some member states, particularly some concerned group of member states, are discussing [this] among themselves," Mr Ban said.
The reaction among diplomats to this unprecedented decision has been one of shock and confusion, the BBC's Nada Tawfik reports from the UN.
France's UN ambassador Gerard Araud said: "We think that Saudi Arabia would have brought a very positive contribution to the Security Council, but we do also understand the frustration of Saudi Arabia."
"The fact is that the Security Council has been unable to act now for more than two years," Mr Araud said, according to AFP.
However, Russia's foreign ministry called the move bewildering, and said Saudi Arabia's criticism of the UN Security Council about its actions over Syria "is particularly strange".
Saudi Arabia has previously expressed frustration at what it sees as an international failure to act on Syria, where it staunchly backs the rebels.
The announcement came hours after Saudi Arabia was elected for the first time to one of the 10 rotating seats on the Security Council.
The non-permanent members sit on the council for two years, along with the five permanent members - the US, the UK, France, China and Russia.
As well as accusing the council of "double-standards" and demanding reform, the Saudi foreign ministry pointed to its failure "to find a solution to the Palestinian cause for 65 years", which had led to "numerous wars that have threatened world peace".
It also criticised the UN's "failure" to rid the Middle East region of weapons of mass destruction, including nuclear weapons.
And it accused the UN of allowing the Syrian government "to kill its own people with chemical weapons... without confronting it or imposing any deterrent sanctions".
The UN Security Council last month finally broke a two-and-a-half year deadlock on how to deal with conflict in Syria after voting unanimously to adopt a binding resolution on ridding the country of chemical weapons.
Saudi observers say Riyadh would have been working for years to gain a place on the UN Security Council, so such a decision would have to have been made at the very top of the kingdom's leadership.