The UK and the European Union have failed to bridge the gap on the Northern Ireland Protocol after the latest round of Brexit negotiations. 

British government minister David Frost was in Brussels on Friday to discuss the key part of the Brexit Withdrawal Agreement with his European counterpart. 

"We have seen no move at all from the UK side. I find this disappointing and once again, I urge the UK government to engage with us sincerely," said the European Commission's Maros Sefcovic at a press conference after the talks wrapped up. 

"I see next week as an important one. We should focus all efforts on reaching a solution as soon as possible," he said, adding that he will travel to London for another meeting with Frost next Friday.

A UK government spokesperson said Frost "underlined that progress had been limited and that the EU's proposals did not currently deal effectively with the fundamental difficulties in the way the protocol was operating." 

"In the UK view, these gaps could still be bridged through further intensive discussions," the spokesperson added.

The UK and European Commission have been locked in tense negotiations over the Protocol in recent weeks. Under the terms of the Brexit agreement, Northern Ireland kept certain EU rules in areas such as food standards, allowing goods to flow into the Republic of Ireland (and therefore the EU single market) without border checks.

However, the UK says it's now causing major disruption and is demanding significant changes to the agreement. The EU has offered to negotiate but hasn't budged on a key issue – oversight of the Protocol by the European Court of Justice. 

As negotiations drag on, speculation is mounting about the UK triggering "Article 16" before the end of the year. This clause allows either side to unilaterally suspend parts of the Protocol. While it kick-starts an arbitration process, the EU could also be forced to start preparing retaliatory measures.

Arriving at the European Commission headquarters in Brussels on Friday morning, Frost wouldn't give any "timescale" for how long talks will continue. 

Frost also travelled to Paris this week to meet France's European Affairs Minister Clement Beaune over the UK's other Brexit-related spat – fishing rights. 

While Beaune described the talks on Thursday as "useful and positive," an agreement still needs to be reached. The two ministers are due to speak again next week.

Due to Brexit, fishing boats from France and other EU countries now require a license from the UK government to operate in British waters.

The UK says 96 percent of French applications have been granted so far, but Paris is pushing for more.