Gerry Adams has accused the SDLP of a “monumental blunder” in spurning a nationalist general election pact.
The Sinn Fein president claimed the SDLP had facilitated the unionist voting alliance in four Westminster constituencies in Northern Ireland.
The rival nationalist party has said it will not enter a nakedly sectarian arrangement.
Speaking on Sundday in Co Tyrone at the election launch for Westminster candidate, Michelle Gildernew, Mr Adams said: “The recently announced unionist electoral pact for the Westminster election is a negative alliance.
“It is aimed at preventing equality of citizenship, frustrating political progress and imposing a Tory austerity agenda.
“Unfortunately, the SDLP leadership has actively facilitated this by refusing to talk to Sinn Fein about how to counter the threat to pro-Agreement, progressive politics.”
The DUP and UUP agreed candidates to fight East Belfast, North Belfast, Newry and Armagh and Fermanagh and South Tyrone.
DUP leader Peter Robinson said he wanted to ensure a strong unionist voice in what is likely to be a hung parliament.
Sinn Fein proposed a nationalist deal in response.
Mr Adams said: “It is a monumental strategic blunder by (SDLP leader) Alasdair McDonnell to spurn engagement with Martin McGuinness on this crucial issue.
“His elevation of petty self-interest above the wider needs of society and the future of the political process is a failure of political leadership.”