A civil court has sentenced an online activist to six months in prison on charges of insulting the Gulf nation's king in Twitter posts, the official news agency said Thursday.

The activist, whose name was not released, was among four people arrested last month for allegedly defaming Bahrain's monarch in cases that mirror other social media crackdowns by Gulf Arab rulers. Court rulings on the three other Twitter activists are expected next week.

The official Bahrain News Agency said that in addition to the sentence, the court on Thursday ordered the activist's laptop and mobile phone confiscated.

Bahrain has been hit by unrest for nearly 21 months as the island's Shiite Muslim majority seeks a greater political voice in the Sunni-ruled kingdom that hosts the U.S. Navy's 5th Fleet.

The prosecutions have brought strong criticism from media freedom groups — as has the government's announcement Tuesday banning public demonstrations.

The ban is the most sweeping attempt to quash the kingdom's anti-government uprising since martial law rules went into effect during the early months of unrest last year. It sharply increases pressure on political groups from the Shiite majority.

Shiites comprise about 70 percent of Bahrain's 525,000 citizens, but claim they face systematic discrimination such as being denied top political and security posts. The Sunni monarchy has made a series of concessions — including giving more powers to the elected parliament — but opposition groups say the reforms do little to loosen the ruling family's hold on power.

U.N. Secretary-General Ban Ki-moon on Thursday joined the U.S. government in criticizing the move by Bahrain's rulers.

The U.N. chief said the restrictions violate international human rights standards, including respect for freedom of expression, peaceful assembly and association, U.N. deputy spokesman Eduardo del Buey said.

"The secretary-general believes these restrictions could aggravate the situation in the country and urges the government of Bahrain to lift them without delay," he said.

Ban reaffirmed that the only way towards greater stability and prosperity is an inclusive national dialogue that addresses the legitimate aspirations of all Bahrainis, del Buey said.