In London, Western officials have announced "substantial progress" in talks with Iran, while also pledging that any potential nuclear deal "must be comprehensive, durable and verifiable."
British Foreign Secretary Philip Hammond said on Saturday after meeting his counterparts from Germany, France and the US that nuclear talks with Iran were progressing well, but also stressed that "we will not do a bad deal that does not meet our red lines."
The four ministers issued a joint statement after their meeting: "We agreed that substantial progress had been made [with Iran] in key areas although there are still important issues on which no agreement has yet been possible. Now is the time for Iran, in particular, to take difficult decisions."
Frank-Walter Steinmeier of Germany arrived for the negotiations on Saturday evening, along with Laurent Fabius of France and US Secretary of State John Kerry.
Together with China and Russia, the four countries are trying to reach a framework deal with Tehran by the end of the month that would restrict parts of Iran's nuclear program in exchange for the lifting of some international sanctions. A full agreement is expected by the end of June, despite opposition from Israel and Saudi Arabia, as well as a group of Republican politicians in the United States.
Kerry, Rouhani cautiously optimistic
Earlier on Saturday, Kerry expressed cautious optimism over Iran's nuclear talks. However, he admitted that there were significant impediments in reaching a deal with Tehran, adding that it was time for tough choices. "We are not rushing...but we recognize that fundamental decisions have to be made now and they don't get any easier as time goes by," he said.
According to the US secretary of state, talks with Tehran made "substantial progress" - but "gaps remain."
Fabius stressed on Saturday that it is necessary to reach an agreement all the regional powers, such as Turkey and Saudi Arabia, could trust. A nuclear-armed Iran would initiate a "catastrophic" Middle East, he told the French radio broadcaster Europe 1.
Amid international efforts to reach a nuclear deal with Tehran, Iran's Supreme Leader Ayatollah Ali Khamenei claimed that Washington was "bullying" his country and accused the US of seeking to foment instability in the Middle East.
"They raise the issue of an atomic bomb. They know themselves that we are not pursuing nuclear weapons. But they just use that as an excuse to pressure the Iranian people," he told a crowd on Saturday in the northeastern holy city of Mashhad.
Also Saturday, Iranian President Hassan Rouhani declared that differences persisted in nuclear talks with the West, but he didn't rule out the possibility of an agreement.
The West suspects Iran of seeking the ability to produce atomic weapons, which Tehran denies.
das/msh (AP, AFP, dpa)