The tradition, the Feast of Fire, goes backs thousands of years to Zoroastrian times and has been banned in Iran in recent decades because of its non-Islamic roots. The opposition had called for its celebration this year as a sign of protest. The supreme leader, Ayatollah Ali Khamenei, issued a decree saying the feast “has no religious basis and is harmful and must be avoided,” the government Web site reported. The celebration includes jumping over fires in the evening, followed by the Iranian version of trick-or-treating, when young people cover themselves head to toe in chadors and bang spoons on pots as they knock on neighbors’ doors for candy. Two men who had also received death sentences for their part in the December protests were executed last month, just ahead of another holiday, the 31st anniversary of the Islamic revolution. Since a disputed presidential election in June set off enduring unrest, the opposition has timed some of its protests to holidays. The December protests came during Ashura, the commemoration of the martyrdom of Ali, grandson of the Prophet Muhammad. The six people whose sentences were announced Monday were among nine convicted of waging war against God by demonstrating during the commemoration. The death sentence for one was confirmed last month, and he was identified weeks later as a student, Mohammad-Amin Valian, 20. The International Campaign for Human Rights in Iran, a New York group, warned this month that he was “in danger of imminent execution.” On Sunday, in another gesture that appeared intended to intimidate the opposition, a crowd of about 50 people who support the government chanted and threw red and green paint at the Tehran apartment building of an opposition leader, Mehdi Karroubi, according to an interview with Mr. Karroubi’s wife posted on Sahamnews, Mr. Karroubi’s Web site. It was the second pro-government demonstration at the home of Mr. Karroubi, an outspoken government critic and one of the candidates in the disputed June election. Their son, Ali Karroubi, was arrested briefly on Feb. 11, before the anniversary of the revolution, and has said he was tortured. The Feast of Fire precedes the Iranian New Year, which falls on March 21 this year. As is traditional, some prisoners are released around that holiday. One was Kian Tajbakhsh, an Iranian-American scholar who was in Iran working on a book when he was arrested after the June protests. He was convicted of spying and given a 15-year sentence, which was reduced to five on appeal. He was released “temporarily” on Friday on $800,000 bail, said a family member who spoke on condition of anonymity.