The call for a republic is set to further raise tensions in the Gulf country [EPA]

Three Shia opposition groups in Bahrain have announced their intent on toppling the Sunni monarchy and setting up a republic.

The declaration on Tuesday is likely to raise already inflamed tensions in the country, ahead of a planned march on the royal court.

Labelled the "Coalition for a Bahraini Republic," the group said in a statement that they "declare a tripartite coalition between the Wafa, Haq and Bahrain Freedom Movement that has chosen to fight for a complete downfall of the  regime, and the establishment of a democratic republic in Bahrain".

"The coalition believes that the main demand of the popular revolution is the downfall of the current oppressive regime and the establishment of a democratic republic that expresses the desires of the people."

Anti-government protests in the Shia-majority, Sunni-ruled country entered the 23rd day on Tuesday, amid a wave of pro-democracy unrest that has gripped the region for weeks and toppled regimes in Egypt and Tunisia.

Other Bahraini opposition groups, including the main Shia Wefaq group, have stopped short of demanding outright regime change, instead calling for major reforms including an elected parliament "with full legislative powers".

"We are different in the demands, but it doesn't mean we can't cooperate,"  Haq leader Hassan Mashaima told AFP news agency.

"I believe that ... there is not much difference between a constitutional monarchy like in Holland or in Britain, there is not much difference between  that and a republic."

''Real' constitutional monarchy

Wefaq and other opposition groups have called for a "real" constitutional  monarchy to be established in Bahrain.

But Mashaima said that he does not trust that a constitutional monarchy along those lines would be implemented even if it was promised.

"This is why we chose changing the regime to a republic."

Meanwhile Wefaq said that it and six other opposition groups had held talks on Monday with the pro-government National Unity Assembly and agreed on the importance of working against sectarian tension.

National Unity Assembly leader Sheikh Abdul Latif al-Mahmud told reporters after the meeting that there was agreement with the opposition on the need for "strategic solutions to problems faced by Bahrain".

He said constitutional reform was a priority.

Demonstrators continue to keep vigil in hundreds of tents in the capital Manama's Pearl Roundabout, which has become the focal point of the protests.