Secretary of State John F. Kerry said Saturday that now is the time to make “hard decisions,” as he left the latest round of talks for consultations before next week’s final push for an agreement over Iran’s nuclear future.

Kerry said progress had been made over five days of talks in Lausanne and that a comprehensive agreement is within reach.

“We have not yet reached the finish line,” he said. “Make no mistake. We have the opportunity to do this right. It’s a matter of political will and tough decision-making. It’s a matter of choices. And we must all choose wisely in the days ahead.”

Speaking in an auditorium at the Olympic Museum, Kerry’s remarks sounded at times like the culmination of the past 16 months of negotiations, even though one more round remains before a March 31 deadline for an agreement outlining the elements of a final deal.

“The stakes are high,” he said. “The issues are complicated, highly technical and interrelated. We don’t want just any deal. If we had, we could have announced something a long time ago.”

Acknowledging that significant differences remain, Kerry said: “We recognize that fundamental decisions have to be made now, and they don’t get any easier as time goes by. It is time to make the hard decisions. We want the right deal that would make the world, including the United States and its closest partners, safer and more secure. That is our test.”

Kerry later stopped in London to coordinate strategy with the foreign ministers of Britain, France and Germany, as well as the foreign policy chief of the European Union. Underscoring the sense of urgency as the deadline approaches, the envoys all met in a VIP lounge at Heathrow Airport, rather than going to more formal surroundings in central London.

After meeting in the lounge, the diplomats stood together while British Foreign Secretary Philip Hammond read a joint statement:

“Now is the time for Iran, in particular, to take difficult decisions,” it said, citing both “substantial progress” and unresolved issues.

The statement said none of the negotiating nations would accept a deal that was not “comprehensive, durable and verifiable.”

“We are at an important moment in the negotiations,” the statement said. “If we are able to resolve all the main issues, technical work will follow to convert a framework into a detailed text.”

Kerry had already spoken by phone with the foreign ministers of Russia and China. All are negotiating partners of the United States in the Iran talks, a group collectively known as the P5 plus 1.

Graphic: Iran's potential nuclear capability

Iranians, meanwhile, seem to be getting mixed signals on the talks.

President Hassan Rouhani said Saturday that negotiators in Lausanne made headway that can be the basis of a final deal Iran can live with.

In remarks on the presidential Web site and reported by the official IRNA news agency, Rouhani cautioned that differences remain but said none was impossible to resolve.

However, the final say is up to Iran’s supreme leader, Ayatollah Ali Khamenei. And he publicly criticized the United States in a speech Saturday, marking the Persian new year, Nowruz.

As people in the crowd in the northeastern city of Mashhad shouted, “Death to America,” Khamenei accused the United States of using “bullying tactics” and economic pressure in an attempt to get Iranians to reject Islamic rule, according to a Reuters report from the city.

“Of course, yes, death to America, because America is the original source of this pressure,” he said. “They insist on putting pressure on our dear people’s economy. What’s their goal? Their goal is to put the people against the system.”

Khamenei also accused President Obama of dishonesty for saying in a videotaped Nowruz message to Iranians that some people in both Iran and the United States oppose a nuclear deal with Iran.

“There is no one in Iran who opposes settlement of the nuclear issue,” according to an account in the Iranian news agency Tasnim. “Giving in to the U.S. bullying and imposition (of its will).”

The next round of nuclear talks is scheduled to begin Thursday in Lausanne.