The European Commission Vice-President Maroš Šefčovič has accused the UK's Brexit Minister, Lord David Frost, of "political posturing".
Writing in The Mail on Sunday Lord Frost said "urgency" was needed from the EU to resolve the issues in the Northern Ireland Protocol.
The protocol is the deal between the EU and UK agreed as a way to avoid a hardening of the Irish land border.
Mr Šefčovič was speaking on Sunday on the BBC's The Andrew Marr Show.
He said that in his meetings with stakeholders in Northern Ireland the message had been to "focus on the key priorities and problems we have to solve".
He said the four problems he heard repeatedly were supply of medicines, a need to reduce customs formalities, reduce SPS (agrifood) checks and find a way to better involve Northern Ireland stakeholders in the dealings of the protocol.
"If we can find a way to solve these problems we are opening the way for a smooth operation of the protocol," he said.
"My feeling is the Northern Irish people want us to work together to look for a way for the Protocol to work properly and in the smoothest possible way," he added.
Lord Frost has said the solution is that "goods which both we and the EU agree aren't going to leave NI should not be treated as if they were moving from one country to another because they are not and goods going into Ireland should be checked in the Irish Sea to protect the EU's single market and avoid a hard border".
Mr Šefčovič said the key word in Frost's article was the word "urgency".
"Sometimes I feel in our meetings I am the only one pushing for urgent solutions," he told the programme.
"We have been putting proposals on the table on solving the uninterrupted supply of medicines to NI since June and I remember Lord Frost telling me that what is important for him is not only content but also process.
"I was waiting to see if he can deliver on that solution jointly and I have to say that until today that has not been the case," he said.
"If we would still be in the mode of political posturing and bringing new problems to the table, I don't think we will solve the most pressing issues for Northern Ireland and so we may be acting alone to ensure the Northern Ireland people have the medicines they need," he added.
Both men said that talks on Friday had brought some progress, with Mr Šefčovič saying there had been a "change of tone" and Lord Frost saying "significant gaps remain".
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