Resolving the political crisis in Northern Ireland has been made more difficult by the snap general election, parties have warned.
SDLP leader Colum Eastwood accused Theresa May of throwing "a grenade into the middle of our peace process".
Sinn Féin's northern leader Michelle O'Neill said the prime minister had shown a "blatant disregard" for the people of Northern Ireland.
Meanwhile, the main unionist parties are to discuss an electoral pact.
Ulster Unionist Party MP Tom Elliott told BBC News NI that talks with the Democratic Unionist Party would take place in the next few days to secure the "best agreement around some constituencies".
On Wednesday, MPs voted overwhelmingly to back the prime minister's call for a snap general election on 8 June - three years ahead of schedule.
Meanwhile, talks continued in Northern Ireland between Stormont's political parties and the British and Irish governments in a bid to restore the collapsed institutions.
Mr Eastwood said that by calling a general election, Mrs May had thrown the process into uncertainty and it would now be "very difficult" to reach a deal by the deadline of early May.
"She has sacrificed the opportunity for progress," he said.
"That doesn't mean we are walking away, we are still here. We will keep meeting until we can get this power-sharing establishment up and running.
"The British government seems to have walked away from it. They need to get back around the table."
Ulster Unionist Party leader Robin Swann MLA said power-sharing talks had been put under added pressure by Mrs May's move.
"But we shouldn't allow things locally to drift further," he said. "It is already disappointing that Westminster is legislating for something as local as the regional rate.
"We need to see local decision makers doing the job they were elected to carry out."
Ms O'Neill said the general election announcement was about "the Tory party's self interest".
"Sinn Féin is ready to fight this election. We will go out and engage with the public who voted in the majority to stay in the European Union," she said.
"This election is not about orange and green, it is about Brexit and opposition to the Tory party's policies."
Sinn Féin currently has four MPs but they do not take their seats in the House of Commons, in protest against British rule in Northern Ireland.
Northern Ireland is represented by 18 MPs at Westminster; the DUP is the largest NI party with eight MPs.
DUP deputy leader Nigel Dodds said the announcement of a general election during the Stormont discussions was "unfortunate".
However, he said the DUP was ready to form an executive in Northern Ireland.
"We do not believe in setting red lines and preconditions above issues affecting health, education and the future of our public services. So that executive is being held up by others," he added.
Alliance leader Naomi Long said it would be "disgraceful" for any party to use the impending general election to stall or withdraw from the current talks process.
"However, the chances of a deal this side of June 8 have now become more remote," she added.
Long-running rows over a proposed Irish language act and deep divisions over how to deal with the legacy of the Troubles are holding up a deal.
Secretary of State James Brokenshire has warned there will either be direct rule from Westminster or another election if no agreement is reached by early May.