Peter Robinson and Martin McGuinness met David Cameron on Friday.
There is no confirmation on the content of the talks, but it is understood they are likely to have covered financial matters related to the talks process.
NI Secretary Theresa Villiers says she believes a deal is possible next week.
Sinn Féin leader Gerry Adams has predicted that the talks at Stormont will conclude soon.
The round-table talks between Northern Ireland's political parties are aimed at finding a resolution to the crisis at Stormont.
The political row was triggered by a police assessment that IRA members were involved in the murder of former IRA man Kevin McGuigan Sr last month.
Police said the IRA still existed, but added that it was not engaged in terrorism.
Sinn Féin said the IRA has "left the stage".
The talks are also focussing on the issue of welfare reform.
The Northern Ireland parties had agreed on a welfare reform deal in December but Sinn Féin withdrew its support in March.

The Northern Irishman edged ahead of Welsh rival Chaz Davies on the last of the 22 laps to clinch his third successive win in Australia.
Rea's British and Kawasaki team-mate, Englishman Tom Sykes, was third.
"It was a little bit like a bicycle race and no-one wanted to put their nose in front," Rea, 30, said.
The champion's victory - his 39th in WSB - ended Davies' six-race winning streak from 2016.
Rea is one of four riders to clinch back-to-back Superbike titles but is aiming to become the first to win three in a row.
He still lies two titles behind Carl Fogarty's record of four championship successes.
Toomebridge man Eugene Laverty, who is back in the series after two campaigns in the MotoGP paddock, finished eighth on his Milwaukee Aprilia.
There will be a second Superbike race at Phillip Island on Sunday.
The first and deputy first ministers have held a private meeting with the prime minister in London, Downing Street sources have confirmed.
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Defending world champion Jonathan Rea has won the opening race of the 2017 Superbike World Championship at Phillip Island.