Bahrain has imposed emergency-style rules banning all protest gatherings in the Gulf kingdom.

It has also threatened legal action against groups considered to be backing escalating demonstrations.

The order, announced by the Interior Ministry, is the most sweeping attempt to quash the kingdom's anti-government uprising since martial law rules were in effect during the early months of unrest last year.

The move sharply increases pressure on political groups from Bahrain's Shia majority, which has led the protests seeking a greater political voice in the Sunni-ruled nation.

Tougher steps against opposition groups could raise complications for the US and other Western allies that have stood by Bahrain's monarchy during more than 20 months of unrest.

The US has important military bonds with Bahrain, which hosts the US Navy's 5th Fleet, but it also has called for increased efforts at dialogue to ease the tension.

Shias comprise about 70% 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.

More than 50 people have been killed in Bahrain's unrest since February 2011.

The Interior Ministry said Bahraini society was "fed up" with near non-stop demonstrations and clashes and "there was a need to put an end to them".

Bahrain's government has permitted limited protests and marches, but much of the violence occurs outside the authorised gatherings.

It added that any "illegal rally or gathering would be tackled through legal actions against those calling for and participating in it".

This warning appeared aimed particularly at the largest Shia political group, Al-Wefaq, which has organised many opposition marches. Another rally is planned for Friday.

An Al-Wefaq official, Hadi al-Musawi, said the order was "against international human rights".

Other Gulf states have placed limits on political expression amid worries that movements inspired by last year's Arab Spring uprisings could threaten their ruling systems.

Last week, Kuwait banned all public gatherings of more than 20 people following opposition protests before parliamentary elections on 1 December.