Police released a member of Kuwait's Al-Sabah ruling family on Sunday after holding him for several days over remarks on Twitter in which he accused the authorities of corruption and called for political reforms, a rights activist said.

Kuwaiti authorities detained Sheikh Meshaal al-Malik Al-Sabah on Thursday, Anwar al-Rasheed, secretary general of the Gulf Forum for Civil Societies, told Reuters.

While Kuwait has one of the most open political systems in the Gulf, the head of the ruling family, the emir Sheikh Sabah al-Ahmad Al-Sabah, has the final say in political matters.

Elected lawmakers and media commentators often attack the government and senior ruling family members over policy although criticism of the emir is forbidden.

"(Sheikh Meshaal) is unhappy about the situation in Kuwait and the royal family...In some tweets he talked about corruption. These are very hard messages from someone who is in the royal family. That's why they arrested him," Rasheed said.

"If I talk like him, nobody listens because I am one of the Kuwaiti people but coming from the royal family, it is hard for them," he added.

Attempts to reach officials from Kuwait's Interior Ministry were unsuccessful. Rasheed said police had interrogated Sheikh Meshaal but did not charge him over the comments on the micro-blogging site which is hugely popular in Kuwait.

Political power in the major oil producer is concentrated in one branch of the Al-Sabah family, the descendents of Mubarak al-Kabeer.

Sheikh Meshaal comes from another branch of the family and tensions between different groups have helped fuel political instability. Meshaal told his 26,000 followers on Twitter he aimed to stand for parliament in the next election.

He criticised authorities for corruption and ignoring the will of the people, and described "a constitution full of holes that is not being followed", in a Twitter message on July 23. http://twitter.com/meshalmalek

In another sign of Kuwait's sensitivity to certain topics on Twitter, authorities arrested a politician and charged him with inciting sectarian strife, a statement from the ruler's headquarters said on Tuesday.

Former MP Mohammad al-Juwaihel was charged with trying to "compromise the social fabric and instigate tribal and sectarian divides," the statement on state news agency KUNA said.

"We condemn with deepest censure the statements and remarks made through social and other media which offended a group within the Kuwaiti society," it added.

"The law shall be imposed without any slack against...all who compromise national unity and harmony."

Juwaihel, a centrist politician, was accused of insulting one of Kuwait's tribes on Twitter, news site al-Rai reported.

Although Kuwait has largely been spared the sectarian violence between Sunni and Shi'ite Muslims that has flared elsewhere in the region, the government is constantly aware of the potential for tensions to boil over.

Shi'ites are thought to number between 20 to 30 percent of Kuwait's 1.1 million nationals. Some occupy senior positions in parliament, the media and business. The ruling family is Sunni.

In June a Kuwaiti court sentenced Hamad al-Naqi, a Shi'ite, to 10 years in jail for endangering state security by insulting the Prophet Mohammad and the Sunni rulers of Saudi Arabia and Bahrain on Twitter.

In April, Sunni writer Mohammad al-Mulaifi was sentenced to seven years in jail and fined nearly $18,000 after a court ruled that he had posted falsehoods on Twitter about sectarian divisions in Kuwait and had insulted the Shi'ite faith.

The recent cases have prompted the government and lawmakers to push for new laws for social media that mirror those governing Kuwait's traditional media.