Bahrain imposed emergency-style rules Tuesday banning all protest gatherings and threating legal action against groups considered backing escalating demonstrations and clashes in the strategic Gulf kingdom.

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

Tougher steps against opposition groups could raise complications for Washington and other Western allies that have stood by Bahrain's monarchy during more than 20 months of unrest. The U.S. has important military bonds with Bahrain, which hosts the U.S. Navy's 5th Fleet, but it also has called for increased efforts at dialogue to ease the tensions.

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.

More than 50 people have been killed in Bahrain's unrest since February 2011. Among them were two policemen who died this month from injuries suffered in attacks by firebombs and explosives.

A statement by the Interior Ministry said Bahraini society was "fed up" with near nonstop 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 authorized 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 Shiite political bloc, Al-Wefaq, which has organized many opposition marches. Another rally is planned for Friday.

An Al-Wefaq official, Hadi al-Musawi, struck a defiant tone, calling the Interior Ministry order "against international human rights."

Other Gulf states have placed limits on political expression amid worries that movements inspired by last year's so-called 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 Dec. 1.