Manama: Bahraini police fired tear gas at anti-government protesters on Friday as they tried to prevent clashes with armed loyalists and as tensions soared in the kingdom.

Thousands of demonstrators chanted slogans against the king as they marched toward a square near the royal palace in Manama where a group of pro-regime loyalists waited with clubs, swords and metal pipes.

The demonstrators hurled stones at riot police who responded with tear gas, according to an AFP reporter at the scene.

Some of the protesters had earlier offered flowers to the police and chanted "Peacefully, peacefully!" to ensure the demonstration did not descend into violence.

In the nearby Refaa area, the pro-government group chanted "The people want Khalifa Bin Salman," referring to the long-time prime minister whose ouster the opposition demands.

"Long live the Bahraini monarchy," they yelled.

Bahrain has been gripped by protests calling for political change since February 14.

There has been a debate within the opposition over whether to go ahead with the march to the royal palace in Refaa, with moderates saying it will only provoke sectarian tensions.

Protesters do not know exactly where the call for the palace march originated, though it appears to have come from one or more of various youth groups.

Demonstrators continue to keep vigil in hundreds of tents in Manama's Pearl Square, which has become the epicentre of anti-government protests.