An investigation is to be launched into alleged irregularities at polling stations in the North during Thursday's election.
Electoral officers apparently differed in their interpretation of regulations concerning the closing time of polls.
In at least two counting stations, votes were reportedly cast after the official 10 p.m. deadline. Elsewhere, people who arrived before closing time complained of not being allowed to vote.
The chief electoral officer, Mr Denis Stanley, was last night investigating reports that people were allowed to vote in certain polling stations after 10 p.m.
Mr Stanley said legislation made it clear that no ballot papers could be issued after 10 p.m.
"That means if someone has been given a ballot paper before 10 o' clock, they can complete it and put it in a box but they can't be issued with a ballot paper after 10 o' clock."
Despite reports of irregularities, Mr Stanley said election results would stand unless a successful electoral petition was launched by an aggrieved candidate. In such cases the result would be declared invalid and a by-election called, he said.
Throughout the North, there were reports of voters arriving on time at polling stations but being unable to cast their votes.
Mr Stanley rejected claims that more staff should have been employed at polling stations and pointed out that 3,500 officials were on duty on Thursday.
"We have asked for detailed reports of all of these allegations," he said. "We will want to see what lessons can be learned, and if there should be a dual election again in the future.
"The large percentage of the day went very well and it wasn't until the evening we came into this difficulty. We had tried to avoid a late evening rush."