Security forces in Bahrain have used tear gas and armoured vehicles to drive back hundreds of protesters advancing toward a heavily guarded square that was once the centre of pro-reform demonstrations in the Gulf nation.

Witnesses said hundreds of demonstrators marched to Pearl Square in Bahrain's capital Manama after a funeral procession on Friday morning for the 78-year-old father of an opposition leader. 

According to the Bahrain Centre for Human Rights, Ali Hasan al-Dehi was beaten to death by riot police on Wednesday while returning to his home in the village of Dehi. Opposition groups claim he died as a result of his alleged treatment by police.

The United States, whose Fifth Fleet is based in Bahrain, called on all sides to exercise restraint. It urged the government to be fully transparent in the investigation of what happened to al-Dehi.

"We, the US, would encourage full transparency as this case proceeds and we obviously call on everybody to exercise restraint," Victoria Nuland, a US state department spokeswoman, said in Washington.

"It is a fragile time in Bahrain as all sides wait for the Bahraini independent commission of inquiry report."

The head of the commission, which was set up to investigate allegations of human rights violations in Bahrain during months of unrest, on Monday was quoted as saying that he had found evidence of systematic torture.

But the Bahraini ministry of health denied the accusation, saying that al-Dehi had died from a heart attack after he fell unconscious at his home.

Al-Dehi was the father of Hussein al-Dehi, who is the deputy-head of the main Shia opposition group. Authorities said he died of natural causes.

After his funeral, hundreds of mainly Shia Bahrainis tried to make their way toward the former Pearl Roundabout - the site where anti-government protests first began.

With assistance from troops from other gulf countries, the government ended the protests with a violent crackdown that reportedly killed dozens.

Video and images uploaded on social media websites on Friday appeared to show police cars driving at protesters in several locations.

Nabeel Rajab, president of the Bahrain Centre for Human Rights, said the government had blocked roads to try to prevent people from attending the funeral ceremony. 

Bahrain is hoping to conclude an arms deal with the United States but the purchase could hinge on the results of the commission investigating this year's unrest and claims by Shias of abuse they suffered during martial law.

Source: Al Jazeera and agencies