Iran's authorities appear to be taking measures to prevent citizens from gathering at the tomb of Cyrus the Great, the first king of Persia, in celebration of Cyrus Day.

The ancient king's big event is to be held on October 29, which many believe is the day he conquered Babylon.

Reports suggest that the authorities are erecting a fence and imposing restrictions to limit the number of people who visit the pre-Islamic king's tomb, located in the ancient city of Pasargadae in the central province of Fars.

Last year, thousands of Iranians assembled in the desert at the site of the ancient monument to celebrate the unofficial holiday. Many chanted nationalistic slogans, including "Iran is our country, Cyrus is our father."

Reports say up to 300 people were detained at the peaceful gathering. The New York-based Center for Human Rights In Iran reported that some 70 people were later sentenced to prison terms ranging from three months to eight years.

Earlier this week, Hamshahrionline reported ahead of Cyrus Day that those visiting the tomb would encounter additional restrictions. "The conditions for visitors at Pasargadae have changed in recent days," the news site reported on October 24.

"According to eyewitnesses, traffic cards have been issued for the inhabitants of Pasargadae to prevent cars and nonresidents from entering the ancient compound on [October 29]," the report added.

Several Iranians told RFE/RL's Radio Farda that they had received threatening text messages warning them that those attending the "illegal" Cyrus Day gathering could face prosecution.

The BBC's Persian service reported that it had received similar reports from its audience.

It wasn't clear who sent the messages.

Earlier this week, a Radio Farda listener recorded a video in Pasargadae in which workers appear to be erecting a fence around Cyrus's Tomb.

The listener said that local people had said that "security bodies" ordered that the fence be erected to prevent people from celebrating Cyrus Day at the location.

Iranians are fascinated and very proud of their ancient pre-Islamic past, which was also celebrated under the reign of Mohammad Reza Shah Pahlavi.

Iran's clerical establishment has been putting more emphasis on the country's Islamic heritage, while trying to downplay the nation's pre-Islamic history.

Cyrus, who ruled in the 6th century B.C., is celebrated by many Iranians for founding the Achaemenid Empire and establishing the first universal declaration of human rights.

The 2016 gathering at Cyrus's Tomb in Pasargadae appears to have been the largest in recent years.

The rally angered hard-line conservatives, including senior cleric Nuri Hamedani, who blasted those celebrating Cyrus as "counterrevolutionaries" and said that they had been chanting slogans normally reserved for Supreme Leader Ayatollah Ali Khamenei.

Earlier this week, the Cultural Heritage Organization of Fars Province dismissed as "false" a statement making the rounds on social media that announced that the Pasargadae historical complex will be closed on October 27-29 to prevent "abuse" by "antirevolutionary groups."

Fatemeh Rezai, who is in charge of public relations for the organization, said a decision had not yet been made about "the activities" at the Pasargadae complex in late October.