Bahrain's Shiite opposition raised the pressure on Monday on Grand Prix organisers to cancel the ritzy Formula One show for a second year in a row, amid fears over the fate of a jailed hunger-striker.
The youth group of the "Revolution of February 14" called for "three days of anger" in the Gulf kingdom from April 20 to 22, and also launched a campaign on Twitter to prevent the race which is scheduled for April 22.
Support has been increasing for jailed Shiite activist Abdel Hadi al-Khawaja who has been on a hunger strike for two months, and on Monday his lawyer expressed fears that he may even be dead.
"It is unlikely that the race will be held if Abdel Hadi Khawaja or Hassan Mashaima is harmed," Khalil al-Marzuk, a leader of Al-Wefaq, the main Shiite opposition bloc which does not endorse cancelling the race, told AFP.
Mashaima, head of the radical Shiite opposition movement Haq and like Khawaja serving a life sentence for allegedly plotting against the monarchy, has cancer.
The opposition accuses the authorities of preventing him being treated.
The government, keen to host the event, has offered repeated assurances that the race would be held safely, after it was cancelled last year because of opposition protests.
Last year's event was called off in the wake of a mid-March crackdown on the protests demanding democratic reforms that would challenge the power of the Sunni Al-Khalifa ruling dynasty.
Protests led by the country's majority Shiites began on February 14, 2011 in the wake of the Arab Spring.
But their movement was put down a month later by the government with strong support from other Gulf states, led by Saudi Arabia.
There are fears that new violence could erupt if Khawaja dies in custody because of the hunger strike he began on the night of February 8-9.
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Formula One supremo Bernie Ecclestone has insisted that an outbreak of fresh violence will not affect this year's race, and motor racing chiefs said they were in "daily contact with the highest authorities" in Bahrain.
"The FIA is the guarantor of race security and in each country counts on local authorities to guarantee this security," the FIA said on Friday.
"On this point, we have been regularly assured by the highest authorities in Bahrain that all the security challenges are under control."
The Sakhir circuit's boss, Sheikh Salman bin Isa al-Khalifa, have an assurance of safety for participants, adding on BBC Radio 4 that "the country has suffered, the economy suffered. All that happened is very sad but we can not go back and rewrite history. We must learn from them and forge ahead."
Formula One teams are reluctant to race in Bahrain, according to two British newspapers on Monday, amid mounting concerns about human rights abuses and Khawaja's fate.
Hundreds of F1 engineers, mechanics and catering staff have been issued with two return tickets from Sunday's grand prix in China -- one for Bahrain and one for Europe and home if the race is cancelled, The Times said, without quoting sources.
Bahraini security forces have strengthened their deployment and witnesses say surveillance cameras have been installed in Manama and outside Shiite villages.
The Sakhir circuit, south of the capital Manama, is near villages where Shiites have held near daily anti-government protests.
"The demonstrations directed at F1 will escalate sharply if Khawaja dies, increasing the risk of deadly clashes with security forces," warned Human Rights Watch's Joe Stork, deputy director for Middle East and North Africa.
The New-York based HRW has not called for the race to be cancelled, but Stork added that the situation was deadlocked since the crushing of the uprising last year.
"There have been no political concessions (from the authorities) and very little implementation of the key recommendations" of an independent commission investigating the suppression of the dissent, he said.
Front Line Defenders, a Dublin-based non-government organisation of which Khawaja is a member, also warned on Sunday about the risk to his health.
"It is impossible to imagine that the Bahrain Grand Prix will go ahead if Abdel Hadi al-Khawaja dies on hunger strike in prison," said the organisation's executive director, Mary Lawlor, in a statement.