"We can be 100% sure that the protocol is the solution, not the problem," European Commission vice president Maroš Šefčovič told Euronews.
The EU has warned against changing rules governing post-Brexit trade between the Republic of Ireland and Northern Ireland.
The UK says the rules, set out in the Northern Ireland Protocol, are not working and need to be refined.
Under them, Northern Ireland has continued following EU rules to avoid border checks with its southern neighbour. But because Great Britain now doesn't follow Brussels regulations, there have been new red tape demands on certain goods entering Northern Ireland from the British mainland. It has led to disruption and some shortages, prompting calls from Northern Ireland and London to change how the protocol works.
But in an interview with Euronews, Maroš Šefčovič, vice president of the European Commission, appeared to reject the idea of making any changes.
"I think we have to be all very cautious about breaching international law, an agreement we just signed," he said.
"We can be 100% sure that the protocol is the solution, not the problem. The protocol is the only way we can avoid a hard border on the island of Ireland."
In order to move forward, Šefčovič urges all sides to dial down the "heated rhetoric" and create a more "conducive atmosphere".
He says the EU is "always ready to deliver" on its commitments but the UK must realise the effort is a "two-way street".
"I believe if the UK used all the flexibilities which we already agreed upon in December, then also the implementation of the protocol would be much easier," he said.
Underlining the importance and scope of EU-UK relations, Šefčovič vowed to increase efforts on the ground and reach out directly to civil society, business representatives and political leaders to ensure the correct implementation of the protocol.
Protocol under renewed scrutiny
The Northern Ireland Protocol came under the spotlight last month amid a row over COVID-19 vaccines.
After AstraZeneca announced delays in its deliveries, Brussels moved to put export controls on vaccines made in the EU.
In doing so, it triggered — before quickly backtracking — article 16 of the protocol, which is essentially a way of pulling an emergency cord on the agreement.
The move was immediately condemned, especially because it was made without consulting London, Dublin or the Northern Ireland Assembly. The European Commission was forced into an embarrassing U-turn and quickly erased the problematic provisions from the final version of the exports control scheme.
However, political sensitivities were inflamed and the torrent of criticism still resonates.
"It was a mistake which we recognised, we corrected it within three hours," said Šefčovič. "It never led to the activation of Article 16. We apologised for it, and we are sorry."
Asked about the demands from Irish MEPs for further clarification regarding the decision-making process that led to such mistake, he added that the European Commission "has already responded" and the best answer now would be to make the protocol work in practice.
Commissioners 'absolutely united' behind von der Leyen
Referring to the EU's slow rollout of COVID-18 vaccines, Šefčovič said the situation would be "much worse, much bleaker if we wouldn’t have a unified European approach."
He said EU commissioners are "absolutely united" behind President Ursula von der Leyen, who has been the target of criticism over vaccines.
"Our president took enormous responsibility upon herself and the college that we became the forefront for managing the health crisis from the point of view of vaccinations," he said.
"And I think that was a very important decision, very much appreciated by the leaders in our member states."
"We are also very honest about what we could have done better. Maybe we trusted the vaccine suppliers too much that they would be able to deliver what they actually signed up to the contracts. Maybe they had to be, let's say, more forceful in making sure that all the contracts [that] have been signed would be respected from day one."
Šefčovič says Brussels will now focus on working with new potential suppliers, like Johnson & Johnson and Novavax as well as on increasing the production capacity of EU-based vaccine plants and speeding up the authorisation process to deal with the coronavirus variants.
"We want to have the early contact with the producers, with the scientific community, to make sure that if some boosters or adjustment to the vaccines is needed, that we would be very fast."
He said he was convinced Europeans would see an increase in vaccine deliveries by the end of quarter one and the beginning of quarter two of 2021.