A journalist eyewitness and a family member said at least four Ukrainian activists were missing after being led away by pro-Russian militants in two separate incidents in and around Crimea.
Oleksy Byk from the internet journal Glavkom said he saw some 20 gunmen around two women kneeling on the ground with their arms tied near the village of Armyansk on the unofficial border between Crimea and the rest of Ukraine on Sunday.
"Their belongings were scattered on the road," said Byk, who saw stickers in support of the Maidan protest movement.
The Maidan protesters who toppled ex-president Viktor Yanukovych are now campaigning for Ukrainian unity after Russian forces and pro-Kremlin gunmen seized control of Crimea.
A spokesman for the pro-EU Euromaidan movement in Kiev, Svyatoslav Yurosh, said that three, not two, women were seized. He said the three, activists Oleksandra Ryazhtseva and Kateryna Butko and journalist Olena Maksymenko, had been travelling together.
"We are very concerned that this can be very dangerous to their lives," he said.
Yurosh believed that the women were at a camp near the improvised checkpoint on the unofficial border between Crimea and the rest of Ukraine.
In a second reported incident, activist Sergiy Kovalskiy said his father Anatoliy Kovalskiy and a second man, Andriy Shchenkun, were taken away as they picked up supplies for a pro-Kiev rally in the peninsula's main city Simferopol. He said that the people who took them away were "wearing black and orange ribbons, they were self-defence forces" - an informal grouping of pro-Kremlin militants that often accompanies Russian troops deployed in Crimea.