Bahrain on Sunday said mourning for Iran's late supreme leader Ayatollah Ali Khamenei is prohibited during Ashura commemorations this month.
This year's observance, a time of mourning for Shiite Muslims, will be the first since Mr Khamenei was killed by an Israeli air strike on the first day of the Iran war. The Iranian leadership has for years associated the ritual with its revolutionary ideology.
Since coming under attack by Iranian drones and missiles, Bahrain has launched a wide-ranging crackdown on that ideology, arresting dozens of people with suspected links to the Islamic Revolutionary Guard Corps (IRGC). The kingdom said last month that it was investigating extremist influences in schools and charities.
At a meeting on Ashura preparations on Sunday, the Interior Minister Rashid bin Abdullah Al Khalifa said the rituals would take place in "tense security conditions". He said Iran's "political project wrapped in a religious guise" was calling people's loyalty in Bahrain into doubt.
The minister "stressed that mourning for the supreme leader is prohibited and punishable", Bahraini official media said. He said people should follow Bahraini rituals older than the Iranian revolutionary ones.
"We will not leave room for those who work to politicise the occasion, violate public order, break the law, raise banners and chant slogans linked to regional agendas and organisations that contradict the constants of the nation and its identity," he said.
For Shiite Muslims, Ashura is a commemoration of the death of one of the Prophet Mohammed's grandsons, Imam Hussein, in the seventh century.
Like other Gulf states, Bahrain has had hundreds of Iranian missiles and drones fired at it since the war began. Its air defences have been tested again in the past week, puncturing a US-Iran ceasefire.
As part of the ensuing crackdown, 41 people were arrested last month on suspicion of working for the IRGC. Several people have been jailed for life, and King Hamad has spoken of "betrayal that cannot be forgiven" by those found to have collaborated with Iran.
