Talks on Iran’s nuclear programme have entered their “endgame”, Germany’s Foreign Minister Frank-Walter Steinmeier has said.
Negotiators from six world powers are attempting to strike a deal with Iran to restrict its nuclear programme in exchange for sanctions relief.
The parties have set a deadline of the end of March to reach an agreement.
Iranian Foreign Minister Mohammad Javad Zarif said that progress was being made.
Mr Steinmeier said as he arrived in the Swiss city of Lausanne for the talks: “These are decisive days before us after nearly 12 years of negotiations with Iran.
“The endgame of the long negotiations has begun.”
After meeting Mr Steinmeier and French Foreign Minister Laurent Fabius, Mr Zarif said: “I think we can in fact make the necessary progress to be able to resolve all the issues and start writing them down in a text that will become the final agreement.”
He has already met US Secretary of State John Kerry in Lausanne.
Mr Fabius added a note of caution, saying: “We have moved forward on certain points, but on others not enough.”
Britain, China and Russia are expected to join them over the weekend, with comprehensive talks due Sunday.
They have set themselves a deadlines of 31 March for a political framework agreement and 30 June for a final deal.
Iran insists its nuclear programme is for peaceful purposes but world powers fear it has military ambitions.
Some of the most contentious issues remain unresolved, says the BBC’s Barbara Plett Usher.
Potential sticking points in the nuclear talks are thought to include the pace at which sanctions would be lifted, how long the deal will last and how much of Iran’s nuclear facilities will be open to inspection.