For her part Ms O'Neill said: "The Tory Party's reckless Brexit agenda offers nothing to the people of the North who are being dragged out of the European Union against our will".
Sinn Féin and the SDLP avoided the opportunity to take political pot-shots at each other, instead maintaining the emphasis on Brexit.
Theresa May's announcement came during a pause in talks to restore devolved government in Northern Ireland.
During a phone call with the British Prime Minister last night, Taoiseach Enda Kenny emphasised that a return to direct rule in Northern Ireland should not be contemplated.
Sinn Fein's voter drive will have an early test.
While Sinn Féin's leader in Northern Ireland Michelle O'Neill said the election will be an opportunity for voters to oppose Brexit and reject Tory cuts and austerity.
Alliance leader Naomi Long said it would be "disgraceful" for any party to use the election to stall or withdraw from the Stormont talks process.More news: Walcott: Nothing can keep Ozil down
In a statement Mr Flanagan said he is "concerned" about the impact of the snap elections.
Some commentators suggested the June 8 election could reduce resistance to regional elections. The First Past The Post voting structure for general elections means that electoral pact are more encouraged than in local/assembly elections.
"It tells you all you need to know about Theresa May that she would call a snap Westminster election in the middle of intense efforts to restore power-sharing government here", he said.
"From the beginning of her tenure as British prime minister she has shown very little but disinterest and disdain for this place".
The party will be seeking to build on its Assembly campaign success - even though there is no question it will continue its boycott of Westminster.
But with tensions in the province already high over Brexit and with unionists, who hold some of their 11 Westminster seats by a slim margin, anxious about the rise of Sinn Fein, this general election is likely to make politics in Northern Ireland even more turbulent than it has been in recent months.