Brussels must stop sulking over the UK's decision to leave the European Union and work to make Brexit a success, Boris Johnson's Europe adviser has said.
Lord Frost says the EU should "shake off any remaining ill will towards us for leaving, and instead build a friendly relationship, between sovereign equals".
Last week the Prime Minister infuriated Brussels when he unilaterally extended the grace period for supermarkets' goods and parcels from the end of this month to October, prompting threats of legal action from Brussels. The grace periods mean procedures and checks are not yet fully applied.
The move sparked a fresh row with the EU, which is jointly responsible with the UK for the Northern Ireland Protocol governing trade and new border checks in the province.
But writing for The Telegraph, the Cabinet Office minister blames the escalating tensions on the EU's threat to impose a hard border on the island of Ireland in January.
Lord Frost, who personally negotiated the Brexit trade deal and joined Mr Johnson's Cabinet last month, says the EU's behaviour "has significantly undermined cross-community confidence in the Protocol".
He writes: "As the Government of the whole of our country we have to deal with that situation - one that remains fragile. That is why we have had to take some temporary operational steps to minimise disruption in Northern Ireland. They are lawful and are consistent with a progressive and good faith implementation of the Protocol.
"They are about protecting the everyday lives of people in Northern Ireland, making sure they can receive parcels and buy the usual groceries from the supermarket."
Lord Frost, who made his maiden speech in the House of Lords last Thursday, also says the UK's decision to break away from an EU scheme on coronavirus vaccines to order its own supplies instead was a tangible example of the benefits of Brexit.
He writes: "I have always believed that the gains of controlling our own affairs outweigh the short-term adjustments. That is what Britain has chosen.
"And we are already seeing the results of that choice. Opting out of EU vaccine procurement has had extraordinary results. It will enable us soon, I hope, to cast off all the shackles of lockdown and to return to the full freedom and normal life which a free people have every right to expect."
Lord Frost, pictured below, also says that Brexit will allow the UK to play a bigger role on the world's stage.
"In recent years it was too often claimed that Britain was no longer interested in playing a major international role. I never believed that. The British people are internationalist and want to make a difference in the world."
He adds: "With Boris Johnson as Prime Minister, our agenda is one of an outward-looking country, confident we can work with others towards common goals. That is our hope for our ties with our European friends and allies too. I hope they will shake off any remaining ill will towards us for leaving, and instead build a friendly relationship, between sovereign equals.
"That is what I will be working towards, acting constructively when we can, standing up for our interests when we must - as a sovereign country in full control of our own destiny."
Lord Frost's comments were praised by the leaders of the European Research Group of Conservative MPs.
David Jones, the group's deputy chairman, said: "The EU has displayed significant bad faith, ranging from the intemperate anti-British sniping of Mr Macron's Europe minister, Clément Beaune, to the extraordinarily aggressive and unjustified action of banning the export of vaccines to the UK.
"This is in clear breach of the spirit of the Northern Ireland Protocol. The UK can't be expected to stand by while trade is disrupted and supermarket shelves are at risk of emptying.
"David Frost is absolutely right to take proportionate measures."
On Saturday Rishi Sunak, the Chancellor, said officials were working through issues surrounding checks on imports that are due to be introduced on April 1 and July 1.
He said: "If there are problems we are trying to address them. People are adjusting to the new things they have to do. The systems and IT are all on track but we are keeping everything under review to make sure it is all as smooth as possible."
Meanwhile, it emerged that the EU is to appeal to the US to allow the export of millions of doses of AstraZeneca's Covid-19 vaccine to Europe to make up for its shortfall of supplies.