The U.K. and the European Union remain locked in a standoff over how to implement the Brexit deal in Northern Ireland, despite more than three hours of talks between top officials on Thursday.

Cabinet Office Minister Michael Gove and European Commission Vice-President Maros Sefcovic held a rare face-to-face meeting in London, which their teams described as “frank but constructive.”

But they did not resolve the key disagreements over trade that have soured the U.K.-EU relationship in the six weeks since Brexit was completed.

Gove and Sefcovic promised to “intensify” their work “with the shared objective to find workable solutions on the ground,” according to a joint statement released after Thursday’s talks concluded.

Since the Brexit transition period ended on Dec. 31, tensions have flared between the two sides over a series of issues, including trade in financial services, the supply of Covid-19 vaccines, and the flow of goods between mainland Britain and Northern Ireland.

The part of the U.K.’s exit deal covering Northern Ireland effectively kept the region in the EU’s customs union and single market and imposed checks on goods moving across the Irish Sea from Great Britain.

Those checks are politically abhorrent to some in Prime Minister Boris Johnson’s Conservative Party, as well as Northern Irish politicians who are passionate supporters of keeping their region in a close union with the rest of the U.K. The new arrangements have also caused disruption to commerce in Northern Ireland, with store shelves lying empty as the flow of supplies dried up.

Gove and Sefcovic pledged to meet again by Feb. 24 in an effort to resolve the difficulties. Before then, British and European officials will hear from businesses in Northern Ireland who have complained about disruption to goods flowing from mainland Britain since the U.K. left the EU’s trade regime on Dec. 31.

In their meeting, the two men reiterated their commitment to both the Good Friday peace agreement in Northern Ireland and to the “proper implementation” of the Brexit accord. They said they would “spare no effort to implement solutions mutually agreed” to last year, according to the joint statement.

The European Commission on Jan. 29 briefly threatened to trigger an emergency clause in the Brexit divorce deal to curb vaccine exports to Northern Ireland. That dramatically escalated tensions between the two sides.

Before the meeting, Gove said the Northern Ireland part of the Brexit deal wasn’t working, and called for a reset in the EU’s relationship with Britain. That was rebuffed by the EU, which said Britain needs to honor the promises it made on Northern Ireland as part of the Brexit deal.