Bahraini opposition activists, inspired by the success of street protests in Egypt, plan to demonstrate near the US embassy on Wednesday in defiance of a government ban.

The Sunni rulers of the Shiite-majority Gulf kingdom have assumed sweeping new powers to crush demonstrations but the protest organisers insist they will go ahead.

Amnesty International urged authorities to avoid the use of force under the "draconian" new measures, insisting that the people must have the right to demonstrate peacefully.

Organisers have called on Washington to use its influence with the authorities to ensure that a pro-democracy demonstration can be held on the doorstep of its embassy without bloodshed.

Tiny but strategic Bahrain, just across the Gulf from Iran, is the home base of the US Fifth Fleet and Washington is a long-standing ally of the ruling Al-Khalifa dynasty.

The Bahrain Rebellion Movement, Tamarod, which is organising the planned rally, is less than two months old.

It takes its name and inspiration from the Egyptian Tamarod movement, which spearheaded the nationwide protests that triggered the army's overthrow of Islamist president Mohamed Morsi on July 3.

The Bahraini group announced its formation on the day of the Egyptian coup but it is taking up a cause that inspired mass demonstrations in the capital in 2011 that were put down only with the help of Saudi-led troops.

Neighbouring Saudi Arabia has a Shiite minority of some two million people and is deeply sensitive to any move to empower Bahrain's Shiites.

On August 1, Tamarod posted an open letter asking the US embassy to provide protection for the planned rally, saying it poses "ethical responsibilities" for Washington.

"We hope that you may convey our deep concern to the US State Department and the US Congress to exert a real political pressure on Bahraini regime to avoid any fatal crackdown and bloodshed," the letter said.

The group said the goal of the demonstration was a "real democracy in Bahrain not less than that found in Western countries such as the USA and the United Kingdom."

At least 80 people have been killed in Bahrain since the Arab Spring-inspired pro-democracy protests erupted in early 2011, according to the International Federation for Human Rights.

The main Shiite parties have boycotted parliament for more than two years to press their demand for a genuine constitutional monarchy, in which top ministers are elected , not appointed by the king from within the ruling family.

King Hamad assumed sweeping new powers earlier this month to counter what the authorities say is an upsurge in "terrorism" linked to the Shiite-led protests.

The government banned all demonstrations in the capital, except for officially authorised events outside the offices of international organisations.

The authorities say police stations and patrols have come under bomb attack in Shiite villages outside the capital in recent months.

Veteran Prime Minister Prince Khalifa bin Salman, an uncle of King Hamad, warned on Saturday that the government would not tolerate any threat to public order.

"This island will remain a ember that will burn those who want to jeopardise its security and stability," he said.

"We shall not allow our country to face the chaos, destruction and displacement suffered by other countries," he warned.

The UN Human Rights Office has urged the government to respect the right to peaceful protest.

"We call upon the government of Bahrain to fully comply with its international human rights commitments, including respect for freedom of expression and peaceful assembly, and association," said spokeswoman Cecile Pouilly.

And Amnesty International said it feared the new decrees "will be used to legitimise the use of force to quash peaceful protests."

"For years the authorities in Bahrain have shamelessly sought to stifle freedom of expression, taking increasingly drastic steps to stamp out dissent with complete disregard for international law," said regional director Philip Luther.

Reporters Without Borders also voiced concerns over what it described as a "new upsurge in abusive treatment of journalists" ahead of the rally.

It said two bloggers, two photographers and a cameraman have been arrested since the end of July.

"The authorities plan to impose a news blackout on the 14 August demonstration by jailing netizens and preventing journalists and human rights defenders from visiting Bahrain," it said.