According to a US official on Saturday, Russia and China vetoed a consensus statement that South East Asian nations had draughted for the East Asia Summit, mostly because of disagreements with terminology about the disputed South China Sea.

The official stated that the 18-nation East Asia Summit gathering in Laos on Thursday night was presented with a draft statement that the 10-nation Association of Southeast Asian Nations had reached a consensus on.

“Asean presented this final draft and said that, essentially, this was a take-it-or-leave-it draft,” the official said on condition of anonymity.

The United States, Japan, Australia, South Korea and India all said they could support it, the official said, adding: “The Russians and the Chinese said that they could not and would not proceed with a statement.”

The Russian foreign minister, Sergei Lavrov, told a news conference in Vientiane on Friday the final declaration had not been adopted because of “persistent attempts by the United States, Japan, South Korea, Australia and New Zealand to turn it into a purely political statement”.

A request for comment was not immediately answered by China's embassy in Washington.

The US official acknowledged that there were several points of disagreement, but said the main one was the way it went beyond the 2023 EAS statement in its reference to the United Nations Convention on the Law of the Sea (Unclos).

However, the official said, “there was certainly no language that was getting into the nitty gritty of any particular standoff, no language that was favouring any claimant over any other”.

China claims nearly all of the South China Sea and has stepped up pressure on rival claimants, including several Asean countries, notably the Philippines. Asean has spent years negotiating a code of conduct with Beijing for the strategic waterway, with some Asean states insisting it be based on Unclos.

China says it backs a code, but does not recognise a 2016 arbitral ruling that said its claim to most of the South China Sea had no basis under Unclos, to which Beijing is a signatory.

According to a draft seen by Reuters, the proposed EAS statement contained an extra sub-clause over the 2023 approved statement, and this was not agreed to. It noted a 2023 UN resolution saying that Unclos “sets out the legal framework within which all activities in the oceans and seas must be carried out”.

Another sub-clause not agreed said the international environment, including “in the South China Sea, the Korean Peninsula, Myanmar, Ukraine and the Middle East ... present challenges for the region”.

The Chinese premier, Li Qiang, told the summit Beijing was committed to Unclos and striving for an early conclusion of a code of conduct, while stressing its claims have solid historical and legal grounds.

“Relevant countries outside the region should respect and support the joint efforts of China and regional countries to maintain peace and stability in the South China Sea, and truly play a constructive role for peace and stability in the region,” he said.