Britain's Brexit department has apologised after David Davis visited Northern Ireland yesterday and made an unannounced visit to the border.
The trip by the Brexit Secretary has drawn criticism from Sinn Féin because the area's local MP was not informed.
Mickey Brady, MP for Newry and Armagh, accused Mr Davis of avoiding a meeting with him because he is "afraid to face the truth about Brexit".
A spokeswoman for the Britain's Department for Exiting the European Union said of the lack of notification: "This was an administrative oversight for which we are happy to apologise."
The DUP was not given notice of the trip either, but the spokeswoman said the Northern Ireland Office had been informed ahead of the visit.
Mr Brady's party colleague, West Belfast MP Paul Maskey, said Mr Davis had shown "contempt" for local politicians and not followed protocol in arranging the visit.
He tweeted: "Out of courtesy and protocol he should have informed you (Mickey Brady) as the local MP.
"Shows his contempt to locally elected representatives who know more about the impacts of Brexit than he will ever know."
The trip, made almost two years after the EU referendum, was little more than a "box-ticking exercise", the SDLP's Claire Hanna said.
The South Belfast MLA, who is the party's spokeswoman on Brexit, said Mr Davis should have been open to addressing local concerns during the visit.
She said: "Maybe the minister is troubled that we might actually have asked him if he learned anything and how he plans to stop a hard border here when his government continues to dig its heels in on the customs union.
"This visit was nothing more than a box-ticking exercise. The border shouldn't have just been an afterthought months down the line but should have been a priority for the Brexit Minister."
Following the short trip, during which Mr Davis was escorted by former senior police officer and Co-operation Ireland chief executive Peter Sheridan, he reiterated the British government's determination to avoid a hard border on the island.
Mr Davis tweeted: "As we leave the EU it's essential both the UK and EU do what it takes to keep the border, which I saw this morning, free from physical infrastructure.
"We are determined to get this agreed by October."
As part of the trip Mr Davis visited an autism centre in Middletown in Co Armagh, as well as a nearby food processing company.
He also saw a former customs post between Armagh and Monaghan.
Elsewhere, a spending watchdog has said the UK will have to pay its "divorce bill" of up to £39 billion to the EU even if no agreement is reached on a future trade deal.
Auditor General Sir Amyas Morse said that if parliament approves the withdrawal agreement being negotiated in Brussels in a vote in the autumn, it will become a legally binding treaty regardless of the success of separate trade talks.
Prime Minister Theresa May told the House of Commons in December the cash offer was made "in the context of us agreeing the partnership for the future", adding: "If we don't agree that partnership then this offer is off the table."
But, asked if he believed the payment was conditional on a trade deal, Sir Amyas told the Commons Treasury Committee: "No, that's not my understanding."
He told the cross-party committee: "As I understand this, the treaty - once approved - will pass into law in time for us to leave the EU and then will become legally binding.
"Therefore the payments would fall to be paid no matter what, under international law."