Donald Trump has attempted to dismiss suggestions of impropriety over Vice-President Mike Pence’s stay at his Doonbeg resort in Ireland and US military use of an airport near his Turnberry golf course in Scotland.

Amid a slew of Monday morning tweets attacking enemies and heralding his own achievements, the president said he had “nothing to do” with Pence’s stay and “knew nothing” about official use of the airport near his course.

The House oversight committee has been investigating whether increasing expenditure at the airport and allegations of US military personnel being offered discount deals at Trump’s Ayrshire golf resort represent a violation of the US constitution.

The emoluments clause of the US constitution bars the use of elected office for private gain, and ethics experts have said Trump’s alleged abuse of the clause could in itself constitute impeachable behavior.

On taking office, the president did not fully divest from the Trump Organization, which is now run by two of his sons.

Trump’s own stays at his own properties, most notably Mar-a-Lago in Florida, as well as government and diplomatic use of his hotel in Washington, have raised concerns that he is profiting from his presidency.

At the G7 summit in Biarritz, France last month, Trump raised eyebrows at home and abroad by strongly suggesting the 2020 summit should be held at his golf resort in Doral, Florida.

Pence visited Ireland last week, while Trump stayed at home to monitor Hurricane Dorian and play golf at his course in Virginia. The vice-president stayed at the Trump International Golf Club in Doonbeg, on the west coast. That posed logistical challenges, as the resort is 180 miles away from Dublin, where Pence met the taoiseach, Leo Varadkar.

On Monday morning, Trump wrote that he “had nothing to do with the decision of our great [VP] Mike Pence to stay overnight at one of the Trump-owned resorts in Doonbeg, Ireland”.

However, Pence’s chief of staff, the former White House aide Marc Short, said last week Trump had made a “suggestion” that his vice-president should stay there.

Short also said security concerns and Pence’s desire to visit the home of an ancestor contributed to the decision.

Trump added: “Mike’s family has lived in Doonbeg for many years, and he thought that during his very busy European visit, he would stop and see his family!”

Democrats are also concerned about US military stopovers at Glasgow’s Prestwick airport, which is near the Trump-owned golf course at Turnberry and which has benefited from purchases of fuel by the US defense department. According to media reports, the Turnberry resort has offered visiting air crews free rounds of golf.

Elijah Cummings, chairman of the House oversight committee, wrote in June to the then acting secretary of defense, Patrick Shanahan, to raise “serious conflict of interest concerns” about Trump making money from US military trips to Scotland.

According to Politico, which broke news of the House investigation, the letter said US military spending at Prestwick, the closest airport to Trump’s resort, appeared to have “increased substantially since the election”.

It was reported that the Pentagon had not cooperated with the House investigation. On Sunday night, the US air force ordered a review of all international layover stays.

On Monday, Trump insisted: “I know nothing about an Air Force plane landing at an airport (which I do not own and have nothing to do with) near Turnberry Resort (which I do own) in Scotland, and filling up with fuel, with the crew staying overnight at Turnberry (they have good taste!). NOTHING TO DO WITH ME.”

But the former Bush ethics adviser Richard Painter said on Twitter: “This is yet another violation of the domestic emoluments clause as ⁦[Donald Trump]⁩ takes federally funded profits for his resort. This is yet another ground for his impeachment.”