(CNN) -- A court in Bahrain sentenced 26 people Tuesday to between five and 15 years in prison for offenses connected to recent political unrest, state media reported.
Observers see the court rulings as the latest sign of a growing crackdown on mainly Shiite activists who have staged a series of protests in the Gulf kingdom.
Last week, a group of 20 doctors detained during protests were convicted of attempting to overthrow the government and received prison sentences ranging from five to 15 years, a decision widely condemned by rights groups and the international community.
Bahrain's government issued a statement saying the 26 defendants sentenced Tuesday were not on trial for protesting but for attempted murder and kidnapping, including "brutal attacks on policemen and foreign nationals" during unrest in March.
In one case, nine activists were jailed for 15 years each for allegedly kidnapping a policeman, using force against him and threatening harm for terrorist purposes, the state-run Bahrain News Agency reported, while three were cleared.
One of those convicted, named by the court as Moh'd Habib Al Safaf, also known as Al Miqdad, was also accused of using speeches at demonstrations to instigate harm against police, BNA said.
He was also among four people sentenced to 10 years in prison for kidnapping, beating and stealing from another police officer, the news agency said, with the offenses "committed for terrorism purposes in order to intimidate and terrorize" Bahrain's security forces. Three people were cleared of the charges in that case.
In a third case, another 14 people were sentenced to between five and 10 years for allegedly promoting the overthrow of the government and changes to the political system by use of force and "illegal means" that include holding rallies and illegal demonstrations, calling strikes during working hours and resisting arrest, the agency said.
They were also accused of passing "fabricated pictures and scenes" to external media organizations with the aim of damaging Bahrain's reputation, the news agency said. Nine other defendants were found not guilty.
An increasing number of cases involving civilians arrested during the government's crackdown on protests are now going before Bahrain's national security court, effectively a military court, Amnesty International said Tuesday.
Such trials for civilians should take place in a civil court and follow proper legal procedures, Amnesty Bahrain researcher Said Boumedouha told CNN.
The rights group is concerned that many of those on trial have been arrested without a judicial warrant, held for weeks without access to their families or lawyers, and often see their attorneys for the first time when they appear in court, he said. Many also allege ill treatment and torture while in detention, he added.
In addition, the sentences passed are overly harsh for what are essentially freedom of expression issues -- such as charges of holding illegal gatherings and incitement of hatred of the regime -- rather than criminal offenses, Boumedouha said.
The Bahraini government statement said the national security court hearings have been attended by representatives of human rights groups and the media, as well as the families of both victims and defendants.
The verdicts can be appealed in a civilian court, the Court of Cassation, the statement added.
Condemning last week's decision to jail 20 doctors, the U.S. State Department said it was "deeply disturbed" by the move and urged the Bahraini government to provide fair trials, access to attorneys and judicial transparency.
Protests have lingered in Bahrain for months despite a crackdown by the kingdom's Sunni monarchy, backed by troops from Saudi Arabia and the United Arab Emirates.
More than 30 people have been killed during the demonstrations, in which activists say Bahraini security forces used live ammunition against protesters.
Opposition groups say more than 1,000 people -- mainly Shiites -- have been detained and more than 2,000 have lost their jobs for allegedly taking part in the protests.
CNN's Laura Smith-Spark contributed to this report.