Bahrain's opposition reported the first death in protests timed for Sunday's controversial Grand Prix as a security lockdown was imposed around the Sakhir Formula One circuit and the king said he is committed to reform.
The body of Salah Abbas Habib, 36, was found in Shakhura village, where security forces had "attacked peaceful protesters, brutally beating some of them with various tools and weapons," said Al-Wefaq, the Gulf state's largest Shiite opposition bloc.
It charged that "security forces killed him one day before the final round of the F1 races hosted by Bahrain," without saying how he died.
King Hamad said on Sunday that he was committed to reform, after protests rocked villages in the Shiite-majority kingdom ruled by a Sunni dynasty.
In a statement issued a day after Habib's body was found in the Shiite village in a case the authorities are treating as murder, the monarch said the door was open for talks.
"I also want to make clear my personal commitment to reform and reconciliation in our great country. The door is always open for sincere dialogue amongst all our people," King Hamad said.
"Last month I received the report on progress made on the recommendations of the Bahrain Independent Commission of Inquiry. It confirmed that broad and substantial progress on reform has already been made by the government.
"We must of course continue the pace of reform."
The interior ministry confirmed that "the body of a deceased person was found in Shakhura" with "a wound to his left side" and the case was being considered as murder.
"The government condemns all acts of violence and will ensure the perpetrators of this crime, whoever they may be, will be brought to justice," the ministry quoted Public Security Chief Major General Tariq al-Hassan as saying.
One of Saleh's relatives told AFP that Habib "was taking part in the protest in Shakhura on Friday and was arrested by security forces while other protesters managed to flee."
The relative said there had been no word of him "until we were told that his body was found on Saturday morning."
Witnesses told AFP that security forces fired tear gas and sound bombs to disperse dozens of people who gathered where Habib's body was found.
Thousands of people demonstrated in the Shiite village of Darraz 10 kilometres (six miles) north of Sakhir and chanted slogans including "No concessions!" before dispersing peacefully, an activist said.
A planned march towards the circuit did not go ahead because of a heavy security presence.
Dozens of armoured vehicles were deployed on roads leading to Sakhir, where security gates were set up and bags were thoroughly searched at entrances.
Officials insisted the event was safe, although the Force India team withdrew from Friday afternoon practice on safety grounds two days after four of its mechanics were caught up in traffic near an exploding petrol bomb.
"I think cancelling just empowers extremists," Bahraini Crown Prince Salman bin Hamad Al-Khalifa said on Friday.
"I think for those of us who are trying to navigate a way out of this political problem having the race allows us to build bridges across communities," he told media at Sakhir.
Jean Todt, president of F1's governing body the FIA (Federation Internationale de l'Automobile) said he did not believe the sport's image would suffer because of criticism over the event.
Todt told reporters at Sakhir that he felt F1 had made the right decision.
"The sport has to be healing any kind of problem in the world," he said. "We are not a political body, we are a sporting body. I already hope it will be a great outcome to hold the Grand Prix."
British Foreign Secretary William Hague said he spoke by telephone to his Bahraini counterpart "to call for restraint in dealing with protests including during the Formula One race and to urge further progress in implementing political reforms."
Shiite-led protests have intensified in Bahrain, site of a month-long uprising that was crushed last year, since the ruling Sunni dynasty insisted on going ahead with the Grand Prix.
The February 14 Youth Movement called on social networking sites for "three days of rage" coinciding with the race.
The head of the Bahrain Youth Society for Human Rights, Mohammed Maskati, has said the protests were "a message to those taking part in the F1 race to bring their attention to human rights violations in Bahrain."
Press watchdog Reporters Without Borders (Reporters Sans Frontieres) in a statement deplored what it called "the breaches of press freedom by the Bahraini authorities" ahead of the Grand Prix.
It said King Hamad had "given assurances that Bahrain is an open society but the organisation has recorded numerous breaches of freedom of information since the start of the year."
RSF said last year it ranked Manama "among the 10 most dangerous places for journalists," and said so far it has seen "no significant improvement."