The move is part of the DUP's escalating strategy against Brexit's Northern Ireland Protocol - part of the Brexit deal which was agreed by both sides and is designed to prevent a hard border on the island of Ireland.

The Lagan Valley MLA said: "Today marks the end of what has been the privilege of my lifetime - to serve as the First Minister of Northern Ireland.

"When I first entered the Assembly 12 years ago, I never expected to have the opportunity to lead the government and serve the people of Northern Ireland as first minister.

"Holding this office is one that comes with a heavy responsibility and I have often felt the weight of this burden, to do what is right for all out people."

It is understood senior DUP figures met on Thursday to confirm the timing of Mr Givan's resignation statement.

He had been in post for just over eight months.

Northern Ireland Secretary Brandon Lewis described Mr Givan's decision to resign as "extremely disappointing".

In a statement, Mr Lewis said: "I urge them to reinstate the First Minister immediately to ensure the necessary delivery of public services for the citizens of Northern Ireland."

The announcement comes less than 24 hours after DUP Agriculture Minister Edwin Poots ordered a halt to agri-food checks at Northern Ireland ports.

Mr Givan told reporters: "Our institutions are being tested once again, and the delicate balance created by the Belfast and St Andrew's agreements has been impacted by the agreement made by the United Kingdom government and the European Union which created the Northern Ireland protocol.

"The consent principle is a cornerstone of the Belfast Agreement and it is my earnest desire that all sections of the community will soon be able to give consent to the restoration of a fully functioning executive, through a resolution to the issues that have regrettably brought us to this point."

Speaking after Mr Givan's resignation, DUP leader Sir Jeffrey Donaldson said the Northern Ireland Protocol "represents an existential threat to the future of Northern Ireland's place within the Union".

Irish premier Micheal Martin said he was "deeply concerned" after Mr Givan's resignation, which he described as "a very damaging move".

"The protocol is part of an international treaty agreed and ratified by the UK and EU, to protect the Good Friday Agreement in all its dimensions," his spokesperson said.

"The UK has an obligation under international law, and under its own domestic law, to ensure it meets is obligations under the protocol."

The spokesperson added that Mr Martin has urged the DUP "to return to full engagement with all institutions of the Good Friday Agreement and avoid any action that could damage peace and stability in Northern Ireland".

Mr Givan's departure means Sinn Fein's Michelle O'Neill automatically loses her position as Deputy First Minister - because under Northern Ireland's power-sharing arrangements the roles of first and deputy first ministers are a joint office shared between the two largest parties at Stormont.

It is believed other ministers in the administration will stay in place to oversee their departments.

But the executive will be unable to make any significant decisions - such as agreeing the three-year-budget spending plan which is currently under public consultation.

Sinn Fein had called for an early election at Stormont in response to reports of the DUP first minister's imminent departure.

Mr Poots issued a direction on Wednesday evening instructing officials to stop the agri-food checks at midnight.

However, there has been no confirmation from Stormont officials whether they intend to comply with the order.

On Thursday morning, lorries were still being received at a Department of Agriculture, Environment and Rural Affairs (Daera) checking facility in Belfast Port.

The prime minister's official spokesperson told reporters that checks are continuing despite the order for them to stop, and that the PM would like them to continue while talks with the EU are ongoing.

Read more: What is the Northern Ireland protocol?

Environment Secretary George Eustice later told the Commons there have been "no operational changes on the ground as yet" in terms of Northern Ireland protocol checks.

Mr Eustice added that his officials "continue to liaise" with their counterparts in Northern Ireland, adding that it is "too early to say what the legal position is".

He added the government recognises that the Northern Ireland protocol is "causing significant problems" in its current form and remains "committed" to finding solutions.

The European Commission has said the decision creates "further uncertainty and unpredictability".

"The European Commission has been working tirelessly with the UK government to address practical challenges related to the implementation of the protocol," a spokesperson for the Commission said.

"The decision by the Northern Irish minister for agriculture (Edwin Poots) is therefore unhelpful. It creates further uncertainty and unpredictability for businesses and citizens in Northern Ireland.

"The European Commission will closely monitor developments in Northern Ireland pursuant to this announcement."

The spokesperson added that the Vice President of the European Commission, Maros Sefcovic, will speak to Foreign Secretary Liz Truss on Thursday afternoon to continue negotiations aimed at reducing the number of checks required by the Northern Ireland protocol.

The UK government has said it will not intervene in what it has characterised as a matter that falls to Stormont.