Britain's Brexit minister said a "significant gap" remained in talks with the European Commission over trade with Northern Ireland, and it was ready to take unilateral action if needed.
"We would still like to find a negotiated solution," David Frost said on Twitter after meeting European Commission Vice President Maros Sefcovic in London.
"But the gap between our positions is still significant and we are ready to use Article 16 to protect the Belfast (Good Friday) Agreement if other solutions cannot be found."
The two will meet again next Friday.
(Reporting by Guy Faulconbridge and Paul Sandle; Editing by William Schomberg)
