WASHINGTON - Secretary of State John Kerry will fly to Switzerland on Sunday for the next round of talks over Iran's nuclear program, amid soaring expectations that a historic agreement is imminent.

A cascade of signals from Washington and Tehran suggest the governments taking part in the talks believe they can reach a framework for a deal by late March despite domestic opposition.

In Iran, senior ayatollahs, including the supreme leader, Ali Khamenei, have praised their often-criticized negotiators as patriots working for the good of the country.

Kerry, who has invested a huge amount of effort in direct talks with Foreign Minister Mohammad Javad Zarif, recently stopped in the Persian Gulf region to prepare wary Arab allies for what appears to be the coming deal with their arch foe.

Perhaps tellingly, the U.S. delegation for the upcoming talks includes an additional member. Joining the usual experts on sanctions, arms control, and nuclear proliferation will be Alan Eyre, the State Department's Persian-language spokesman, whose outreach to Iranians has him fielding questions in fluent Farsi on Facebook and Twitter.

While officials have cautioned that a comprehensive deal is not assured, the signposts point to negotiators announcing some sort of general agreement soon, leaving technical details to be worked out by the end of June.

"They're very close," said the Iranian-born Trita Parsi, president of the Washington-based National Iranian American Council. "Momentum is on the side of an agreement being reached. The political capital the two sides have put into this is overwhelming, and would be very, very difficult to walk away."

The talks over Iran's nuclear program began more than a decade ago and proceeded in fits and starts until Hassan Rouhani was elected president of Iran in 2013. In a country staggering under high unemployment and inflation, Rouhani campaigned on a promise of relief from sanctions.

Dozens of sanctions on Iran have been imposed by the United States, the European Union, and the United Nations. They helped bring Iran to the negotiating table, but the timetable for easing them has been one of the main hurdles to finalizing a deal.

Although Kerry has been the most active diplomat involved in talks with Iran, the negotiations are not being conducted by the U.S. alone. The other four permanent members of the Security Council - Britain, France, China, and Russia - plus Germany - also have a say.

And although Congress and the Obama administration have been locked in a dispute over when U.S. sanctions would be lifted, the United States has little or no control over many of the economic restrictions imposed on Iran by the U.N. and Europe. It will fall to the U.N. Security Council to vote on lifting its sanctions.

Some countries with political and economic ties to Iran, notably Russia and China, have balked at additional sanctions. President Obama can temporarily grant waivers on U.S. sanctions, but only Congress can permanently lift them.

Republicans critical of U.S.-Iran nuclear talks contend Obama wants so much to burnish his legacy by negotiating an agreement to restrain Iran from becoming a nuclear-armed state that he is not pushing back against Iranian activities in Iraq, Yemen, Syria, Lebanon, and Bahrain.

At a news conference Saturday in Egypt, Kerry said the ultimate goal is to guarantee that Iran's program will be "peaceful forever."

This article contains information from the Associated Press.