MANAMA – Thousands of Bahrainis demonstrated in the capital Manama on Tuesday demanding regime change in the Gulf kingdom after two protesters were killed in clashes with police.

The protests in a country, which saw deadly unrest in the 1990s between the majority Shiite population and the Sunni ruling family, prompted Formula One boss Bernie Ecclestone to voice concern about next month's Bahrain Grand Prix which opens the new Formula One season.

"This is your only and last chance to change the regime," read a banner carried by protesters who descended on Manama's Pearl Roundabout, shortly after the funeral of one of the two Shiite demonstrators.

The banners and slogans of the Bahraini protesters echoed those of the demonstrators in Cairo's Tahrir Square whose 18 straight days of protest triggered the dramatic end on Friday of Hosni Mubarak's 30-year rule.

Cyber activists outraged by the killing of the two protesters had called for the Manama demonstration on Facebook. MPs from Bahrain's main Shiite opposition bloc walked out of parliament.

Protesters appeared to have turned a deaf ear to King Hamad, who addressed the nation earlier expressing sorrow for the deaths and announcing a ministerial investigation.

Some protesters erected a tent, saying their sit-in will continue until their demands are met.

Demonstrators want a "contractual constitution and a peaceful transfer of power," said MP Mohammed Mezaal, of the Shiite opposition Islamic National Accord Association, whose 18 MPs walked out of the 40-member parliament.

The decision came because of "the deterioration in security and the negative and brutal way in which (authorities) dealt with the protesters, killing two of them," said another of the bloc's MPs, Khalil al-Marzooq.

Fadel Salman Matrouk was shot dead in front of a hospital on Tuesday where mourners gathered for the funeral of Ali Msheymah who died of his wounds after police dispersed a protest in a village east of Manama on Monday, Marzooq said.

He described both men as "martyrs."

King Hamad said he would continue the reform process which saw the restoration in 2002 of the parliament dissolved in 1975. The Shiite opposition has long complained that the elected chamber's legislative authority is shared with an appointed upper house.

"Reform is going ahead. It will not stop," the king said.

The interior ministry said "some of the people participating in the funeral on Tuesday clashed with forces from a security patrol," leading to Matrouk's death.

It also announced the death of a protester late on Monday "due to his wounds" and opened an inquiry into whether police resorted to "unjustified use of arms" in Diya village.

UN High Commissioner for Human Rights Navi Pillay was in no doubt that the force used had been disproportionate.

"I urge the authorities to immediately cease the use of disproportionate force against peaceful protesters and to release all peaceful demonstrators who have been arrested," she said.

Amnesty International's Middle East and North Africa director Malcolm Smart said: "This second killing within two days is both tragic and a very worrying development.

"Like many in the region, those in Bahrain who feel their dignity has been compromised are demanding change. The authorities must listen to these calls, rather than retaliating with violence," the London-based watchdog said.

News of the two deaths prompted activists, who posted pictures of both men on a Facebook page, to call for a huge turnout at their funerals.

Thousands attended Msheymah's funeral in Diya, some chanting that "the people want to oust the regime."

The Formula One chief told London's Daily Telegraph newspaper that it was too early to consider the possibility of calling off next month's Bahrain Grand Prix but said he planned to contact Crown Prince Salman about the risk of protests.

"The danger is obvious, isn't it?" Ecclestone told the paper's online edition. "If these people wanted to make a fuss and get worldwide recognition it would be bloody easy, wouldn't it?"

Washington, which uses Bahrain as home base for its Fifth Fleet, said it urging its allies in the Middle East to open up their peoples like Egypt.

"We have sent a strong message to our allies in the region saying let's look at Egypt's example, as opposed to Iran's example," President Barack Obama said.