High-stakes nuclear talks between Iran and world powers are now in the crucial end game.
But with a March 31 deadline for a framework agreement looming, delegates' ears are ringing from powerful voices away from the negotiating table.
These outsiders have set red lines that weigh heavily on the negotiators, and center on some of the thorniest issues -- including sanctions relief, the fate of Iran's nuclear facilities, and assurances that Tehran won't pursue nuclear weapons.
Whether coming from Iran or the West, those drawing the lines leave no room for concession, and could potentially provide an easy reason for either side to walk away without a deal.
Iran's supreme leader has the ultimate say, but the views of influential hard-liners who oppose a deal will be heard.
Among them are Said Jalili, the chief nuclear negotiator under former President Mahmud Ahmadinejad; the Endurance Front political party; and elements of the powerful Islamic Revolutionary Guards Corps (IRGC).
Their general demands are:
* no deal that would diminish Iran's nuclear enrichment program
* no deal that would leave economic and military sanctions intact
* all sanctions (whether imposed by the United States, European Union, or United Nations) should be lifted immediately
* in the event of new sanctions, legislation would be passed to allow uranium enrichment of 60 percent
Ali Vaez, a senior Iran analyst at the International Crisis Group, says the hard-liner camp's opposition "stems from ideological, geostrategic, or economic interests."
Well aware that Supreme Leader Ayatollah Ali Khamenei has declared his support for the talks, hard-liners have directed their criticism at President Hassan Rohani and Iran's chief nuclear negotiator, Foreign Minister Mohammad Javad Zarif.
In January, hard-liners attacked Zarif for his stroll with U.S. Secretary of State John Kerry during a break in nuclear negotiations in Geneva.
And the same month, an IRGC commander criticized Rohani's engagement with the West.
"Fake revolutionaries, who joined the ranks of revolutionaries to acquire leadership and riches, speak about the necessity to make compromises," said General Mohammad Reza Naqdi.
However, analyst Vaez explains, the hard-line group represents a minority because, for the first time in a decade, Iran's highly factionalized political elite appears to agree on the need for a speedy resolution of the nuclear standoff. Their consent appears to have been steered by popular discontent with the economic malaise brought on by Western sanctions.
"Today in Iran, being seen as an obstacle to diplomacy is not only bad policy, but it is bad politics," says Vaez.
Scott Lucas, an Iran specialist at Birmingham University in Britain and editor of the EA World View website, says even among the hard-liners there is little "opposition to a deal per se, but there is opposition to the type of deal that is struck."
Despite their efforts, hard-liners have failed to mount a serious challenge to President Rohani and his negotiating team.
"The supreme leader has come out strongly in support of the nuclear negotiating team -- calling them the children of the revolution, warning against accusing them of appeasement --and has effectively reined in the critics," says Vaez.
But at the same time, Khamenei has made a number of improbable demands.
The supreme leader's 11 "red lines," outlined in October:
Khamenei has also consistently denounced the United States, even as optimism for a deal rose ahead of the deadline.
Addressing worshipers in the holy city of Mashhad on March 21, Khamenei rang in the Persian New Year (Norouz) by accusing the United States of bullying Iran.
And when shouts of "Death to America" rang out from the crowd, Khamenei didn't exactly try to tamp them down. "Of course, yes, 'Death to America,' he was quoted as saying." Because America is the original source of this pressure."
The International Crisis Group's Vaez explains that "the supreme leader's calculus is informed by one motivation: to make sure that a nuclear compromise does not turn into a slippery slope of compromises that could unravel the system."
Khamenei's 11 red lines, according to Vaez, are "mainly aimed at signaling to the West that Iran is not negotiating from a position of weakness."
As talk of a potential agreement has risen, so have concerns that opponents in the U.S. Congress could hinder a deal.
On March 9, 47 Republican senators sent a letter to Iran's leaders noting that any treaty worked out between the United States and Iran would require ratification by a two-thirds vote in the Senate.
Anything short of that, they wrote, would be considered a mere executive agreement between U.S. President Barack Obama and Khamenei. Such an agreement, they warned, could be revoked by the next agreement or modified by future Congresses at any time.
The White House denounced the letter, while Tehran described it as a sign of Washington's deceitfulness.
Senator Marco Rubio (Florida), a signatory of the letter who is viewed as a potential candidate in the 2016 presidential election, has said that, if elected, he would "absolutely" defy European allies if necessary in order to annul a deal he might inherit from President Obama.
Meanwhile, on March 23, 367 members of the U.S. House of Representatives issued a bipartisan letter highlighting the "grave and urgent issues that have arisen" in relation to the nuclear negotiations with Iran.
Among the concerns cited:
* the size of Iran's current uranium-enrichment program
* its lack of cooperation with international inspectors and the need for an intrusive inspection regime
* the need for "verifiable constraints "on Iran's nuclear program, which "must last for decades
* Iran's "destabilizing role" in the Middle East and its horrendous human rights record
Ultimately, the letter says, "Congress must be convinced that its terms foreclose any pathway to a bomb, and only then will Congress be able to consider permanent sanctions relief."
Recently reelected Israeli Prime Minister Netanyahu has expressed fears that a deal could pave Iran's "path to the bomb," and has not ruled out military strikes against Iran if a deal were reached.
In an address before the U.S. Congress earlier this month, Netanyahu predicted dire consequences for the Middle East and the world if a deal were reached, telling lawmakers that Iran is "gobbling up" nations in the region.
Regional rival Saudi Arabia, meanwhile, has said any deal that allows Iran to enrich uranium could spark an arms race in the Middle East.
Saudi Prince Turki al-Faisal, the kingdom's former intelligence chief and ex-envoy to Washington, told the BBC on March 17 that "whatever comes out of these talks, we will want the same."
The Mujahedin-e-Khalq Organization (MKO), an exiled antigovernment organization considered a terrorist group by Tehran, has been involved in exposing Iran's nuclear activities from the beginning.
The MKO was the first, in 2002, to reveal that Tehran was pursuing a secret program to produce material for a nuclear program. The MKO, a consistent opponent of the regime, has since made a number of unverifiable claims over the years.
Most recently, the MKO accused Tehran of conducting secret research at a Tehran plant with the aim of developing nuclear weapons, an allegation denied by Iran.