At least six Ukrainian activists and journalists opposed to Russia's invasion of Crimea have gone missing in the peninsula.Activists Igor Kiryushchenko, the head of the Ukrainian Republican Party's Crimean branch; Andriy Shchekun, the head of Crimea's Ukrainian Council; and Anatolyy Kovalskiy, the director of the board of trustees of the Ukrainian School in Simferopol, have been active in denouncing the Russian takeover of their region.Kiryushchenko was reportedly abducted on March 10 after participating in a rally held in Simferopol a day earlier to protest the Russian occupation.Members of his party said he called the office and said, "Goodbye, they have come for me."Calls to his mobile phone have since remained unanswered.Kiryushchenko has actively supported Ukrainian troops serving in Crimean military bases seized by pro-Russian forces.Shchekun and Kovalskiy appear to have been abducted in Simferopol on March 9, shortly before the start of the anti-occupation rally. They were among the protest's organizers.According to information gathered by RFE/RL, they were apprehended at Simferopol's train station, where they had gone to pick up a parcel from Kyiv.Several men who identified themselves as vigilantes and members of Russian Unity, the party headed by Crimea's new pro-Russia Prime Minister Sergei Aksyonov, reportedly searched the pair before escorting them to the railway station's police department.A second group of men later took the activists away after police officers declined to formally detain them.Crimean prosecutors said a criminal case has been opened into their disappearance.The Center for Journalistic Investigation, a Ukrainian online publication, reports that the two activists were beaten up and that Aksyonov himself sanctioned their detention.The deputy speaker of Crimea's parliament, Hryhoriy Ioffe, confirmed that Shchekun was briefly taken to the office of Russian Unity on March 9.Kovalskiy's son, Serhiy Kovalskiy, said the pair was being held together at a secret location in Simferopol.Also on March 9, two Ukrainian journalists and a spokeswoman for Automaidan -- a group of motorists supporting the pro-European protests -- went missing as they attempted to enter Crimea near its northern town of Armyansk.Olena Maksymenko, a reporter with "Ukrainian Week," independent blogger Oleksanda Ryazantseva, and Automaidan's Kateryna Butko are not answering calls on their mobile phones.According to Euromaidan SOS, a civil initiative group set up since the protests began in November to monitor rights abuses and track missing activists, the women were detained by local Berkut riot police.The group believes they were handed over to officers from the Sevastopol branch of the SBU, the state security service.Several unconfirmed reports have emerged of other journalists being detained at Crimean checkpoints.