By Kirsty Needham

SYDNEY (Reuters) -Tuvalu, a tiny Pacific nation that scientists predict will be submerged by rising seas, said it is seeking written assurance from the United States that its citizens will not be barred from entry after being apparently mistakenly included in a list of 36 countries facing visa bans.

An internal diplomatic cable signed by U.S. Secretary of State Marco Rubio showed the United States, which has already barred entry for citizens from 12 countries, was considering expanding travel restrictions to the 36 countries, including three Pacific Island states, Reuters and other media reported last month.

Nations on the list would have 60 days to take corrective action, the cable showed.

The news had caused significant concern in Tuvalu, whose population of 11,000 is at risk from rising sea levels, and where a third of residents have applied to an Australian ballot for a landmark climate migration visa.

Tuvalu's ambassador to the United Nations, Tapugao Falefou, said he had been told by a U.S. official that Tuvalu's inclusion on the list was "an administrative and systemic error on the part of the U.S. Department of State". 

In a statement on Tuesday, Tuvalu's government said it had not received any formal notification that it was on the list, and had also been assured by the United States embassy in Fiji it was "an error within the system".

"The Embassy has provided verbal assurances that there are no current restrictions on Tuvaluan nationals entering the United States, and that the matter is being reviewed with authorities in Washington," the statement from Tuvalu's Ministry of Foreign Affairs, Labour and Trade said.

It added Tuvalu was seeking a "formal written confirmation to that effect and continues to engage the U.S. Government to ensure Tuvaluans are not unfairly affected".

The embassy did not immediately respond to a Reuters request for comment.

A U.S. official familiar with visa policy who is not authorized to speak publicly told Reuters "no decisions have been made, and any speculation is premature". 

"Tuvalu's public statement mischaracterizes and omits some of the valid concerns the United States has with travelers from that country," the official added.

The other Pacific Islands listed in the cable were Vanuatu and Tonga.

Tonga's government had received an official U.S. warning, and was working on a response, Tonga media reported.

Vanuatu's government did not respond to a request for comment.

(Reporting by Kirsty Needham in Sydney; Editing by Saad Sayeed)