U.S. President Barack Obama and German Chancellor Angela Merkel have called on Iran to make the necessary decisions to reach a deal over its nuclear program.
The two leaders spoke by phone on March 27 as negotiations between six world powers and Iran continue in Switzerland.
They have set an end-of-March deadline to reach a framework agreement.
U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif are already in Lausanne.
They have been discussing the political framework agreement for days in Lausanne on Lake Geneva.
Speaking on the sideline of the talks on March 27, Zarif said the two sides were not close to an agreement, and that the "other side needs to choose between pressure and political accord."
A Western official close to the talks told Reuters that centrifuge research and enrichment in general remained the most difficult unresolved issue.
However, British Foreign Secretary Philip Hammond was more upbeat.
On a visit to Washington on March 27, Hammond said the parties were "better than half way" to a deal.
Reuters quoted unnamed officials involved in the talks as saying the sides were close to agreeing a 2- or 3-page accord, however other unnamed officials were more cautious.
An unnamed U.S. official said that other foreign ministers from the six-power group --which includes Britain, China, France, Germany, Russia as well as the United States -- will arrive in the coming days.
Iran has been pushing for immediate sanctions relief as soon as a pact is sealed, but White House spokesman Josh Earnest said U.S. President Barack Obama thought that would be "unwise."
Iranian President Hassan Rohani sent a letter to Obama and the leaders of the other countries at the talks, containing, what his office said on March 27, were unspecified proposals on how to reach a deal.
Rouhani also spoke to the leaders of Russia, France and Britain by phone.
According to AP, the negotiations have made progress over the fate of a fortified underground bunker previously used for uranium enrichment.
Officials told AP that the United States may allow Iran to run hundreds of centrifuges at the Fordo bunker in exchange for limits on centrifuge work and research and development at other sites.
With reporting by AP and Reuters