Protests rocked Iran again overnight after a seeming slowdown in recent weeks, with marchers calling for the overthrow of the Islamic Republic, online video posts purportedly showed on Friday. The marches in numerous cities including Tehran that began on Thursday evening and went on into the night marked 40 days since the execution of two protesters last month. Mohammad Mehdi Karami and Seyyed Mohammad Hosseini were hanged on Jan. 8. Two others were executed in December. The protests that have swept across Iran began last September after the death in custody of 22-year-old Kurdish Iranian woman Mahsa Amini for flouting the hijab policy, which requires women to entirely cover their hair and bodies. Videos on Friday showed overnight demonstrations in several neighborhoods in Tehran as well as in the cities of Karaj, Isfahan, Qazvin, Rasht, Arak, Mashhad, Sanandaj, Qorveh, and Izeh in Khuzestan province. An online video purportedly from the city of Mashhad in the northeast showed protesters chanting: "My martyred brother, we shall avenge your blood." Reuters could not verify the videos. The long wave of unrest has posed one of the strongest challenges to the republic since the 1979 revolution. Openly defying the hijab rules, women have waved and burned their scarves or cut their hair. While the unrest appeared to have tapered off in recent weeks, likely because of the executions or the brutal crackdown, acts of civil disobedience have continued unabated. Nightly anti-regime chants reverberate across Tehran and other cities. Youths spray graffiti at night denouncing the republic or burn pro-government billboards or signs on main highways. Unveiled women appear in the streets, malls, shops and restaurants despite dire warnings from officials. Many of the women among the dozens of recently released prisoners have posed unveiled in front of cameras. Authorities have not backed down on the compulsory hijab policy, a pillar of the republic. In recent weeks Iranian media have reported closures of several businesses, restaurants and cafes for failure to observe the hijab rules. Earlier this month, a Tehran pharmacy was ordered to close because "its owner disrespected the person who warned her to observe the hijab", the Iranian judiciary’s Mizan news agency reported on Wednesday. Last week, Iranian officials called on trade unions for stricter enforcement of hijab regulations in Tehran’s stores and businesses. "Improperly" veiled female students were warned last month they would be barred from entering Tehran University, while local media reported that about 50 students were prevented from entering Urmia University in the northwest for flouting the hijab rules. Rights activists say more than 500 protesters have been killed since September, including 71 minors. Nearly 20,000 have been detained. At least four people have been hanged, according to the judiciary. Karami, a 22-year-old karate champion, and Hosseini were convicted of killing a member of the Basij paramilitary force militia. Amnesty International said the court that convicted Karami relied on forced confessions. Hosseini's lawyer said his client had been tortured. Two others were executed on Dec. 8 and 12 respectively. Five women activists released on Thursday said in a joint statement they owed their freedom to the solidarity of "the freedom-loving people and youths of Iran", according to social media posts. "The day of freedom is near," they said.