A court in Bahrain has sentenced 50 Shia Muslims to up to 15 years in prison on charges of forming a clandestine movement, reports say.
The 14 February Coalition has been a key influence behind the Shia-led campaign for more rights in Bahrain which began in 2011.
Bahrain, ruled by a Sunni Muslim royal family, accuses the youth movement of terrorism.
Sixteen defendants were given 15-year sentences, reports say.
Four were jailed for 10 years and the remaining 30 for five, according to a judicial source quoted by the AFP news agency.
Thirty of those convicted plan to appeal. Twenty were tried in absentia for their involvement in the 14 February Coalition, a network of secretive groups that organise protests online.
Prominent among those sentenced was human rights activist Naji Fateel, who was given 15 years, according to the Bahrain Youth Society for Human Rights.
The society alleges he was tortured during interrogation. This, the group says, included electric shocks, simulated drowning and beatings.
Others sentenced include Iraqi cleric Hadi al-Mudaressi and London-based opposition activist Saeed al-Shahabi, AFP reports. Both were tried in absentia.
The charges are also said to have comprised trying to overthrow Bahrain's ruling family.
The head of the rights group, Mohamed al-Maskati, told the BBC that the sentences were "only likely to fuel anti-government unrest".
He said more court cases were likely to come up.
Bahrain has been beset by unrest since 2011 as the series of pro-democracy movements known as the Arab Spring took hold in the region.
Two weeks ago, the Bahraini authorities arrested Khalil Marzook, a leader of the main Shia political society Wefaq, on terrorism charges.
Wefaq and other groups responded by suspending their participation in a national dialogue designed to heal political divisions.
Bahrain is seen by Western powers as strategically important, providing a haven for the US Navy's Fifth Fleet in the Gulf.