Ireland’s president, Michael D Higgins, has triggered a political row with Northern Ireland’s unionists by shunning a commemoration of the island’s partition 100 years ago.

Higgins said he would not attend a church service with the Queen next month to mark the creation of Northern Ireland because the event had become politicised.

Higgins also said the invitation had referred incorrectly to him as the president of the Republic of Ireland, rather than the president of Ireland.

Sir Jeffrey Donaldson, the leader of the Democratic Unionist party (DUP), on Friday accused Higgins of impeding reconciliation and urged him to reconsider. The Ulster Unionist party and Alliance expressed disappointment at the president’s decision. Some called it insulting and disrespectful.

The row caught the British and Irish governments off guard because Higgins, a largely ceremonial head of state who is independent of the Irish government, has often championed reconciliation, including appearing alongside Queen Elizabeth and in 2014 making the first state visit by an Irish head of state to the UK.

It is the most serious diplomatic flare-up in a year-long series of events to mark the creation of Northern Ireland in 1921. Formed from six of Ireland’s 32 counties, it had a Protestant majority that wished to remain under British rule while the rest of Ireland obtained de facto independence.

Sinn Féin and the SDLP, which represent Irish nationalists in Northern Ireland, have shunned many centenary events, leaving the British government and unionists to mark the state’s foundation with a low-key programme.

Higgins had been expected to join the Queen at a religious service in Armagh on 21 October. Earlier this week, it emerged he would not attend, prompting unionists to seek clarification. After several days of silence, Higgins on Thursday briefed Irish journalists who are covering his four-day visit to Rome, where he is due to meet Pope Francis.

The president said the title of the event, which it stated was to “mark the centenaries of the partition of Ireland and the formation of Northern Ireland”, made it inappropriate for him to attend.

“What [had started out as] an invitation to a religious service had in fact become a political statement” he told the Irish Times. “I was also referred to as the president of the Republic of Ireland. I am the president of Ireland.”

Referring to the Queen, he said: “I am not snubbing anyone and I am not part of anyone’s boycott of any other events in Northern Ireland. I wish their service well but they understand that I have the right to exercise a discretion as to what I think is appropriate for my attendance.”

Higgins bristled at DUP claims that this amounted to a snub. “It’s a bit much, to be frank with you. I have gone up to Northern Ireland to take part in events. There often has not been a great deal of traffic down from the DUP people who are criticising me now.”

Donaldson told the BBC on Friday the president’s comments were disappointing and “not conducive” to reconciliation. “Failing to recognise the existence of Northern Ireland does not help anybody.”

The Irish government said it would consider any invitation for a government representative to attend and that the president was free to make his own decision.

In a comment piece for the Guardian in February, Higgins urged all sides to remember complex, uncomfortable aspects of Britain and Ireland’s shared history.