Talks to restore power-sharing at Stormont should "intensify" as there is a "genuine but narrow window of opportunity" to reach agreement, Theresa May and Leo Varadkar have said.
In a joint statement, the British prime minister and taoiseach said it was "imperative" the parties "move without delay to engaging substantively on the shape of a final agreement".
Stormont has been in cold storage for more than two and half years due to a bitter standoff between Sinn Féin and its erstwhile partner in government, the DUP, on issues such as Irish language legislation and the region's ban on same-sex marriage.
A new phase of talks was announced on April 26 and the latest statement from Mrs May and Mr Varadkar said they had been updated on progress by Secretary of State Karen Bradley and Tánaiste Simon Coveney.
"We welcome the constructive engagement shown by all parties to date," they said.
"It is clear to us that the Northern Ireland political parties wish to see the institutions of the Belfast/Good Friday Agreement restored but operating on a more credible and sustainable basis.
"While broad consensus has been reached on some issues, other areas remain to be resolved.
"The secretary of state and tánaiste believe that there is a genuine but narrow window of opportunity to reach agreement in the immediate period ahead and that it is essential to continue and intensify talks to this end.
"As prime minister and taoiseach, we will continue to monitor this progress closely.
"We believe it is imperative that the parties now move without delay to engaging substantively on the shape of a final agreement."
