The European Union on Friday backtracked over threats to restrict vaccine exports to Northern Ireland after London voiced "grave concerns" over the proposed move.

A furious row over shortages of AstraZeneca's COVID-19 vaccine has risked stoking conflict with the UK just weeks after London and Brussels sealed a Brexit trade agreement.

On Friday, the European Union sought to restrict exports of COVID-19 vaccines through the Irish border to the United Kingdom by invoking emergency clauses in the Brexit divorce deal, sending shockwaves through both Ireland and Northern Ireland.

Article 16 of the Northern Irish Protocol allows Britain or the EU to take unilateral action if there is an unexpected negative effect arising from the agreement.

Northern Irish unionists cast the move as an act of hostility, while Irish Prime Minister Micheal Martin sought urgent clarification from European Commission President Ursula von der Leyen.

On the same day, British Prime Minister Boris Johnson told EU chief Ursula von der Leyen of his "grave concerns" after Brussels partially suspended terms of the Brexit deal as part of a vaccine export control scheme.

Johnson talked to the EU head on the phone and "expressed his grave concerns about the potential impact, which the steps the EU has taken today on vaccine exports could have," according to his Downing Street office.

As Britain considered its response, Johnson said the EU had to clarify its intentions to ensure it honored its commitments to Northern Ireland.

A Sky News reporter said the EU had withdrawn its move to override the Northern Irish treaty. Euronews said the whole thing was a "mistake" and an "oversight."

The Commission did not comment when contacted by Reuters for clarification but was expected to make a statement shortly.

The swiftest mass vaccination drive in history is stoking tensions across the world as big powers buy up doses in bulk, and poorer nations try to navigate a financial and diplomatic minefield to collect whatever supplies are left.

Irish border

Preserving the delicate peace in Northern Ireland without allowing the United Kingdom a backdoor into the EU's markets through the UK-Irish 496-kilometer land border was one of the most difficult issues of the Brexit divorce talks.

The EU's action – even if it rescinds the decision – triggered anger.

Northern Ireland First Minister Arlene Foster described it as "an incredible act of hostility." 

"The European Union has once again shown it is prepared to use Northern Ireland when it suits their interests but in the most despicable manner – over the provision of a vaccine which is designed to save lives," Foster said.

The EU move aimed to prevent the open border between EU-member Ireland and Northern Ireland from acting as a backdoor for vaccine supplies into the United Kingdom.

Article 16 was devised as a last resort to alleviate serious disruption to trade in Northern Ireland after Brexit.

The EU, whose member states are far behind Israel, Britain, and the United States in rolling out vaccines, is scrambling to get supplies just as the West's biggest drugmakers slow deliveries to the bloc due to production problems.

The British-Swedish drugmaker AstraZeneca has been caught in the crosshairs after it said last week it would fall short of delivering promised vaccines to the EU by March because of production problems in Belgium.

That has angered Brussels, which has demanded to know why it cannot divert supplies from its British sites that have been producing millions of shots for British citizens.

The European Commission has agreed on a plan to control exports of vaccines from the bloc, including to Britain, arguing it needed to do so to ensure its own supplies.

The Commission said its move to invoke Article 16 was justified to "avert serious societal difficulties" in EU states due to a lack of vaccine supply, the document published on Friday said.

Britain has its own domestic supply chain for AstraZeneca's shot, including rolling it out in Northern Ireland, but it imports the Pfizer vaccine from a factory in Belgium.

Britain had threatened to trigger the Article 16 safeguard measures earlier in the month if there were "serious problems" in supplying supermarkets in Northern Ireland.

(With input from agencies)