Londonderry-Strabane and Belfast cannot both be official European Capital of Culture, it has emerged.
A joint bid by both cities to secure the title for 2023 was launched back in July by the Lord Mayor of Belfast Nuala McAllister and Derry City and Strabane District Council Mayor Maoliosa McHugh.
At a meeting on Tuesday of Derry City and Strabane District Council's Business and Culture committee it was confirmed that only one city can hold the official title.
Speaking to the Belfast Telegraph, vice chair of the committee and UUP alderman Derek Hussey said he had suspected that not everything had been made clear in previous presentations.
"I had my reservation in regard to the joint bid, believing of course that Londonderry had the capacity and the expertise to take forward a bid in their own right," he said.
"But the decision was made within Derry and Strabane District Council to bring forward a joint bid."
Alderman Hussey said that it was now a question of which city would go forward as the official applicant, and what guarantees could be made to the partner city to ensure equal treatment.
The vision from the Londonderry-Strabane side of the bid, Mr Hussey said, was to bring benefits throughout the north-west region, including a cross-border benefit for Donegal.
"The important aspect is to ensure that we have a coherent and understandable submission going to stage two, and one that is mindful of all the partners involved in process," he added.
In a statement, a spokesperson for Derry and Strabane District Council said that the bid was a being taken jointly with Belfast City Council, and that European Capital of Culture guidelines state that "only one organisation can be the candidate city and sign the application form".
"The commitment from the councils is to work together with Europe through culture to make our cities better places for our citizens and future generations. The councils will consider the final detail of stage one bid book in the coming weeks and continue with their strong working partnership," the spokesperson said.
The European Capital of Culture has run since 1985, and - despite last year's Brexit vote - will go to a UK-based city in 2023, with Bristol, Dundee, Leeds, Milton Keynes, Truro and Nottingham also in the competition.
In a guide document published by the EU for countries wishing to apply, it is stated that "cities may involve their surrounding areas", but that "one city must be the lead city for the purpose of accountability and responsibility" and that "the lead city is the official bidder".
Speaking at the launch of the Belfast-Derry bid, Lord Mayor McAllister said: "This joint bid is a fantastic opportunity for us to work together on a project that will benefit everyone. It’s our chance to renew civic pride, put both our cities on the map, showcase and celebrate our cultural excellence, strengthen European connections and act as a catalyst for real change and growth."
A special Business and Culture Committee meeting of Derry City and Strabane District Council will take place on September 22, and it is understood a meeting of Belfast City Council will also be held on that day to discuss the same issue.
In a statement a Belfast City Council spokeswoman said: "Discussions are ongoing regarding the candidate city. Both cities are fully represented in the bid content and we will continue to work in close partnership to ensure that programming and delivery is linked to attract the maximum benefits for each. Both councils will consider papers on the European Capital of Culture bid on 22 September."