VIENNA—Iran's foreign minister and lead negotiator in nuclear talks is known to frequently scream and shout at Western diplomats, including Secretary of State John Kerry, a practice that has caused alarm among bodyguards stationed outside the negotiating room, according to a member of the Iranian diplomatic team who spoke to the Farsi-language press.

Iranian Foreign Minister Javad Zarif—who is scheduled to hold one-on-one talks with Kerry this evening in Vienna—"frequently shouts at Western diplomats" in such a forceful manner that bodyguards have hurriedly entered the negotiation room on occasion worried that an incident might occur, according to one Iranian diplomat involved in negotiations who spoke anonymously with the Iranian press earlier this week.

On one occasion, Zarif's shouts were so loud that a member of the Iranian delegation entered the negotiation room to check on the players, according to the report, which was independently translated for the Free Beacon.

Upon entering, the Iranian official was informed by European Union Foreign Policy Chief Catherine Ashton, a chief western negotiator, that Zarif was just shouting and she had gotten used to it, according to an independent translation of the report.

The report of Zarif's aggressive behavior is consistent with previous reports claiming that Iranian negotiators tend to treat their Western counterparts—particularly the Americans—with scorn.

Iranian diplomat Abbas Araghchi, another member of the negotiating team, is reported to have said in an interview that during past negotiations in Geneva, Zarif "shouted" at Kerry and spoke to him in a way that was likely "unprecedented" in the history of U.S. diplomacy.

Araghchi went on to claim that he and Zarif play the roles of "good cop, bad cop," according to the report, also in Farsi. The two often exchange these roles in a bid to "baffle the Western diplomats" and keep them uneasy, the report claims.

Araghchi further claimed that Kerry said very little after being shouted at by Zarif, except for "one or two very respectful sentences."

Meanwhile, negotiations in Vienna over a final deal continue just one day before a self-imposed deadline for the talks.

While some Iranian officials have said that they refuse to extend the talks any further, Western officials, including Kerry, maintain that serious divisions remain between the two sides.

Both sides appear convinced that it will be impossible to reach a final deal before the Monday deadline.

"Given the limited time left, reaching a comprehensive agreement seems unlikely," an Iranian diplomat told the country's state-controlled media early Sunday.

Desperation on the part of the United States has led to a situation in which Iran feels that it has the upper hand and can act brazenly in talks, according to Saeed Ghasseminejad, an Iranian dissident and associate fellow at the Foundation for Defense of Democracies (FDD).

"The problem with the nuclear negotiations is that everybody knows how desperately this administration wants a deal," Ghasseminejad said. "Nothing good comes out of such a situation. Actually it is [Iranian President] Rouhani who should be desperate to reach a deal."

The United States "has gone too far to meet [Iranian Supreme Leader] Khamenei’s excessive demands only because the administration wants to have a foreign policy legacy beyond the total chaos it has achieved till now; the problem is that what they do only makes things worse," he said.