A prominent opposition figure accused by Bahrain of plotting against the state plans to return from London, an aide said Monday, in a move that could bolster protesters and force authorities into difficult choices.

Hassan Meshaima, head of a group known as Haq, is scheduled to arrive late Tuesday as the embattled monarchy tries to engage demonstrators in talks aimed at easing the week-long series of clashes and marches that have deeply divided the strategic Gulf nation.

A rights activist and supporter, Abbas Omran, confirmed Meshaima's plans, but gave no further details on his objections once he returns after eight months in self-exile.

Meshaima is considered by Bahrain's officials as a potential enemy of the state. He and another London-based opposition leader is being tried in absentia among a total of 25 Shiite activists accused of plotting to overthrow Bahrain's Sunni rulers.

But taking Meshaima into custody risks an angry backlash from protesters, whose uprising forced Formula One organizers to call off next month's Bahrain Grand Prix in a stinging blow to Bahrain's efforts to court top international sporting events.

Meshaima has been in London since June, reportedly receiving treatment for cancer. His group Haq is more considered more radical than the main Shiite political bloc, Al Wefaq, which has so far taken a leading role in the uprising.

It's possible that Meshaima — even if taken into custody — could rally more hard-line elements among the protesters as they struggle to find a common voice.

One group called Monday for the ouster of the entire ruling monarchy. Others, however, have signaled a willingness to let the king and royal family remain but with many of their powers and privileges turned over to parliament.

Tensions are still high in Bahrain after seesaw battles that saw riot police open fire on protesters trying to reclaim landmark Pearl Square last week. At least eight people have been killed and hundreds injured in the clashes since the unrest spilling across the Arab world reached the Gulf last week.

Bahrain holds particular importance to Washington as the host of the U.S. Navy's 5th Fleet, which is the main U.S. military counterweight to Iranian efforts to expand its military influence into the Gulf.

The manifesto from a group calling itself "Youth of Feb. 14" — after the day of the first marches — apparently seeks to raise the stakes of demands ahead of possible talks between the opposition and the monarchy.

"We demand the overthrow of the oppressive Al Khalifa regime," the manifesto said, referring to the ruling royal family. "The people will choose the system they will be subjected to."

To underline their contempt for the monarchy, the protesters set up a chair resembling one belonging to a royal with a sign beneath it that says in Arabic "And does the throne of the oppressor stay?"

It was not clear, however, how much influence the group holds the tens of thousands of protesters that range from students to retirees.

In the statement, the youth group called for authorities to be put on trial for attacks on protesters last week and demanded an elected government. They said the first priority should be the cancellation of citizenship for thousands of foreigners who receive it as part of an effort to change the sectarian balance in the island nation. Few policies anger Bahrain's Shiite majority more than bestowing citizenship to outside Sunnis, mostly Arabs but also from Pakistan and other South Asian countries.

Shiites in Bahrain have often complained of discrimination by the Sunni rulers. The Al Khalifa royal dynasty has been in power for 200 years and has strong backing from other Gulf Arab leaders, who fear that Shiite powerhouse Iran could gain further footholds through the uprising led by Bahrain's Shiites.

The week-long unrest has already affected Bahrain's economy. An international rating agency has cut the government's credit ratings because of concerns about political turmoil and the organizers of the Bahrain Grand Prix canceled the March 13 season-opening race, the kingdom's biggest international event it has hosted annually since 2004.

Crown Prince Salman bin Hamad Al Khalifa — the owner of the F1 contract — said in statement that the kingdom must "focus on immediate issues of national interest and leave the hosting of Bahrain's Formula One race to a later date."

Standard & Poor's cut the ratings Monday for Bahrain's long and short-term sovereign credit ratings, as well as those for the island nation's central bank and the country's sovereign wealth fund.

Hundreds of protesters spent the night in Pearl Square — which has become Bahrain's version of Cairo's uprising hub Tahrir Square — and thousands of government opponents gathered at the site during the day. The mood was upbeat and many appear to be camped there for the long haul, with makeshift kitchens serving meals to those who live in the small tent village.

At several stalls, demonstrators queued for hot tea and joked about the weather, which turned windy and whipped up sand and trash.

Bahrain's rulers have offered talks with opposition groups to try to defuse the showdown, but the opposition appears to be in no hurry to talk with the crown prince who has been delegated by the king to lead the dialogue.

The leaders of the official Shiite opposition said they are not refusing to talk to the crown prince, but want guarantees the rulers' words will be backed by action.

The main opposition demand is the resignation of the government that is responsible for this week's bloodshed and has been led by the same prime minister — the king's uncle — for 40 years.

Other demands include abolishing the monarchy's privileges to set policies and appoint all key political posts, along with addressing longstanding claims of discrimination and abuses against Shiites, who represent about 70 percent of Bahrain's 525,000 citizens.

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Associated Press writer Brian Murphy in Dubai, United Arab Emirates, contributed to this report.

(This version CORRECTS activist name 2nd paragraph. )