US Secretary of State John Kerry and his Iranian counterpart Mohammad Javad Zarif huddled in an upscale Geneva hotel, ahead of full negotiations with global powers here on Sunday.
They are seeking to break a stalemate which has caused them to miss two previous deadlines for a full agreement to rein in Iran's suspect nuclear programme.
Zarif told reporters today's talks were "important."
"I think it will show the readiness of the two parties to move forward to speed up the process."
Past negotiations have stumbled reportedly over Iran's insistence that it retain the right to enrich some uranium -- which can in some cases be used to make an atomic bomb -- for what it says is a peaceful civilian nuclear programme.
There has also been disagreement over global sanctions, with Tehran calling for an end to an iron-fisted regime which has crippled Iran's economy, while the US has insisted on a temporary, gradual suspension.
Negotiators have been tight-lipped about their differences and Zarif would not go into detail when asked about the thorniest matters still clouding the talks.
Kerry has said the aim of his talks with Zarif on Wednesday is to "take stock" and provide guidance for their negotiating teams ahead of fresh discussions by global powers known as the P5+1 here on Sunday.
The top US diplomat, who was accompanied to today's talks by his chief negotiators Wendy Sherman and Bill Burns, also told reporters earlier this week that he hopes to "accelerate the process to make greater progress."
The two teams met for two hours Wednesday morning, broke for a short pause, and then resumed their negotiations.
The new Republican-controlled Congress is already considering a bill which would slap new sanctions on Iran despite attempts by the Obama administration to hold them off.
Washington's UN envoy Samantha Power said on Monday that ratcheting up sanctions against Iran would likely torpedo the negotiations.
