One of Ukraine's most famous MPs, Nadiya Savchenko, has been arrested on suspicion of planning an assault on parliament and supporting a coup.
The ex-military helicopter pilot was detained in parliament after MPs viewed evidence against her and voted to remove her immunity from prosecution.
She has not denied the charges.
She had been feted as a national hero after spending nearly two years in a Russian jail. She was captured fighting rebels in eastern Ukraine.
On Thursday MPs watched a video of her talking to two officers about plans to attack parliament.
She smiled and laughed in response, and did not question the authenticity of the video. She said Ukraine's "corrupt" government did need to be overthrown, but described the plot as a "provocation".
She was granted Ukraine's highest award - the Order of the Gold Star - after her release from jail in Russia in 2016 as part of a prisoner swap.
But on Thursday Ukraine's chief prosecutor Yuriy Lutsenko told MPs that Ms Savchenko, 36, planned "a large-scale terrorist act" in Kiev.
He accused her of doing a deal with the Russian-backed rebels to "obtain the weapons necessary for such an attack, in particular 120mm calibre mortars, small arms, sniper rifles, combat grenades".
In April 2014, pro-Russian insurgents seized a large swathe of Donetsk and Luhansk regions in eastern Ukraine, and later declared self-rule, defying the Kiev government.
Ms Savchenko was captured in the region and sentenced to 22 years in jail in Russia for killing two Russian journalists, charges she denied.
She was pardoned by Russian President Vladimir Putin before her return to Ukraine.
Clashes continue in eastern Ukraine between the rebels and Ukrainian government forces, despite a ceasefire deal. Ukraine and its Western partners accuse Russia of backing the rebels with regular troops and heavy weapons - something Moscow denies.