The District Administrative Court of Kiev ruled yesterday in favour of the Ukrainian justice ministry's lawsuit demanding a ban on the Communist Party, after deliberating on the case for some 18 months.
The ban prohibits any further action by the party, including running in local or national elections.
It is one step closer to extinction for the Communist party of Ukraine following its failure to win any parliamentary seats in last year's elections.
"This move is propelling Ukraine backwards not forwards on its path to reform and greater respect for human rights," the London-based rights group quoted its Europe and Central Asia director John Dalhuisen as saying in a statement.
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Ukrainian Communist Party head Petro Symonenko called the decision "illegal", adding that he intended to appeal the ruling to the European Court of Human Rights.
Last year, Ukraine's then acting president Oleksandr Turchynov accused the Communist party of helping pro-Russian insurgents who rose up against Kiev's new pro-Western leaders after the February ouster of a Russian-backed president.
Support dwindled following the annexation of Crimea by Russia in 2014 and the loss of densely-populated parts of east Ukraine to separatist control.
Kiev is seeking to cut ties with its Soviet past and last year decided to ban most Communist symbols and organisations. Monuments to Soviet officials have also been toppled throughout the country and streets honouring Communist figures renamed.