Arlene Foster has made a unionist election pact meeting "more difficult" by outlining the DUP's position in a newspaper article, UUP leader Robin Swann has said.
The DUP and UUP will meet later about a possible pact for the general election.
Mrs Foster wrote in the Belfast Telegraph that the DUP would not stand in Fermanagh and South Tyrone but wanted a clear run in South Belfast.
Mr Swann said he had not read it but the remarks were "a bit arrogant".
"I'm willing to talk, (but) that attitude isn't helpful at the minute," he told the BBC's Good Morning Ulster programme.
He said the article was "a strange way to start any conversation, by putting down a red line so firm and so adamant before we've even sat down to discuss whether we're going to have a pact or not".
In the last general election, in May 2015, the DUP and UUP agreed pacts in four constituencies, including the UK's most tightly-contested seat of Fermanagh and South Tyrone.
The pact helped Tom Elliott win the seat from Sinn Féin's Michelle Gildernew - she had held on to it by just four votes in 2010.
Mrs Foster said she welcomed that decision and that she wanted to "maximise unionist representation at Westminster".
She added that "there can be no argument the DUP is not only the lead unionist party but the lead party in South Belfast".
"Sadly in 2015, the UUP did not accept that reality but given the results in 2016 and 2017 it cannot now be disputed.
"In 2015, despite having two DUP MLAs to the UUP's one, we stood aside in Fermanagh and South Tyrone to allow Tom Elliott the chance to be elected to parliament."
She added: "Notwithstanding out significantly larger status in the constituency I will not field a DUP candidate at this election."
Mr Swann told Good Morning Ulster: "If Arlene is already ruling out seats and putting up red lines it's going to make any conversation difficult.
"I haven't had a chance to read it, (but) it strikes me as a bit arrogant as well.
"I had hoped to go into this as the leader of the UUP with some sort of hope for unionism - some sort of hope for coming to an agreement.
"But, look, I'm still going to have the conversation, because unionism suffered at the March election. I was hoping there could have been a way forward, I still hope there is."
Last Wednesday, MPs voted overwhelmingly to back the prime minister's call for a snap general election on 8 June - three years ahead of schedule.
It was announced earlier this week that the main unionist parties would discuss an electoral pact.