MANAMA, Bahrain — A security court sentenced eight Shi'ite activists to life in prison Wednesday and issued long jail terms for 13 others in the latest blow by authorities waging a crackdown against protesters seeking greater rights in the Gulf kingdom. Shi'ite crowds blocked roads with sand piles and called for protest marches — suggesting the court decision could spark another round of unrest after months of lockdown-level security by military and police units in Bahrain, which is home to the US Navy's 5th Fleet. The wife of one of the activists said he shouted "Our people demand freedom" as the verdicts were read. The sentences also could imperil US-backed efforts by Bahrain's Sunni leaders to open talks next week with Shi'ite groups, which have demanded an end to the political trials and withdrawal of a Saudi-led regional force helping prop up the Bahrain ruling family. Shi'ite comprise about 70 per cent of Bahrain's population, but claim they face systematic discrimination such as being barred from top government and political posts. The protests — inspired by the wider Arab uprisings — have claimed at least 31 lives and put US officials in the difficult position of both denouncing the violence but standing by the rulers in a key military ally. The Shi'ite activists were charged with trying to overthrow Bahrain's 200-year-old monarchy and of having links to "a terrorist organization abroad."