The Brexit deal will not mean a new border between NI and the rest of the UK, the NI secretary has insisted.
Brandon Lewis said: "We always said there will not be a border down the Irish Sea, there'll be unfettered access for business."
Earlier Downing Street said the deal would mean "limited changes" to trade between GB and NI.
The Irish government and the EU have urged the UK to honour all the terms of the Brexit deal.
Under the deal, reached in October, Northern Ireland will continue to follow EU rules on agricultural and manufactured goods.
The rest of the UK will stop following these rules at the end of 2020.
Additionally, the whole of the UK will leave the EU's customs union but Northern Ireland will continue to enforce the EU's customs code at its ports.
This will mean some new checks and processes for goods moving between Northern Ireland and other parts of the UK.
The UK and EU now have to negotiate the nature and extent of those checks.
At the weekend, the Sunday Times reported UK officials were seeking to evade any new checks on goods passing from Great Britain to Northern Ireland.
The paper suggested Downing Street was working on plans to "get around" the Northern Ireland part of the deal, known as the Ireland protocol.
On Monday, the prime minister's official spokesman said: "The UK signed the Withdrawal Agreement including the protocol last month, we will comply with our obligations."
The spokesman added Boris Johnson had "been clear that beyond the limited changes which are introduced by the protocol, there will be no changes to GB/NI trade".
Taoiseach (Irish PM) Leo Varadkar said the Withdrawal Agreement was an international treaty and he expected the UK to "honour that in full".
"We totally understand why they may want to minimise any checks at the ports and airports in Northern Ireland, we want to do that too," he said.
"But the agreement clearly says if there have to be checks anywhere, they would happen at the ports and airports in Northern Ireland rather than on the land border between north and south."
The EU said implementing what had been agreed would be "very important" for establishing trust between the UK and EU in future negotiations.
Dana Spinant, deputy chief spokeswoman of the European Commission, said: "The Withdrawal Agreement has been signed and ratified by both sides and as such it must be effectively implemented.
"That includes of course the protocol on Northern Ireland and all its constituent parts."
Last month the EU's chief negotiator Michel Barnier said new checks on goods entering Northern Ireland from GB were an "indispensable" consequence of the Brexit deal.
Speaking in Belfast, he added: "In agreeing to the protocol, the UK has agreed to a system of reinforced checks and controls for goods entering Northern Ireland from Great Britain.
"I understand the fears of negative economic fallout expressed by some about these checks.
"But Brexit unfortunately has consequences that we must manage."