(CNN) -- A fourth person who died while in the custody of Bahrain police in recent days may have been tortured, Human Rights Watch said Wednesday, as it called for urgent investigations into the deaths of detainees.

The death of Kareem Fakhrawi, 49, was the fourth detainee death reported by the Bahrain government in nine days, the human rights group said.

He was detained April 3 after going to a police station to complain about a predawn raid on the house of a relative, the agency said. Police reported he died Tuesday.

"Four detainee deaths in nine days is a crime, not a coincidence," said Joe Stork, deputy Middle East director at Human Rights Watch. "The government tells families of detainees nothing about their whereabouts or well-being while they are alive or about the circumstances of their deaths."

At Fakhrawi's funeral Wednesday, a crowd of mourners demanded to see his corpse because of concerns he had been tortured, then took photos and videos of the body, the agency said.

A video of a dead body, purported to be Fakhrawi's, was posted on Facebook Wednesday and showed a badly bruised corpse as people crowded around to take pictures.

The body had ligature marks around one of the ankles and deep reddish-purple bruises on the entire upper arms and on a large part of one thigh. The face was black and blue and blood was on the right side of the neck.

In a posting on Twitter, the Bahrain News Agency said an official at the Bahrain Defense Force Hospital attributed Fakhrawi's death to kidney failure.

Human Rights Watch said its personnel did not see the body in person, but urged a thorough and impartial investigation into allegations of torture.

"Bahrain is flagrantly violating the most basic human rights by arbitrarily detaining hundreds, keeping their whereabouts secret, and covering up the reasons for deaths in custody," Stork said.

The human rights agency did view the body of another person who died in custody -- protester Ali Isa Saqer -- and said it showed signs of "horrific abuse" and torture.

The human rights agency said there may be as many as 430 people who have been arrested in Bahrain in the government's effort to quell protests there.

A member of Human Rights Watch observed Saqer's body Sunday after Bahraini authorities said he died in detention.

"His body showed signs of severe physical abuse. The left side of his face showed a large patch of bluish skin with a reddish-purple area near his left temple and a two-inch cut to the left of his eye," Human Rights Watch said in a statement.

"Lash marks crisscrossed his back, some reaching to his front right side. Blue bruises covered much of the back of his calves, thighs, and buttocks, as well as his right elbow and hip. The tops of his feet were blackened, and lacerations marked his ankles and wrists."

Saqer, 31, died at a detention center in early April, according to the general director of Muharraq Governorate Police. Saqer was being held on charges of attempted murder of policemen while trying to run them over with his car March 13.

Authorities said Saqer was creating chaos at the detention center, and when security forces sought to subdue him, he resisted them and sustained various injuries in the process. He was sent to the hospital, where he later died.

Human Rights Watch said there were at least two other people who have died in the custody of police in Bahrain recently.

United Nations Secretary-General Ban Ki-moon spoke with Bahrain's foreign minister Wednesday about the situation.

"He said he was very concerned about the violence in which demonstrators have been killed or injured," a U.N. statement said. "He called for maximum restraint and caution."

The foreign minister, Sheikh Khalid bin Ahmed bin Mohammed Al Khalifa, recently spoke to CNN about accusations that protesters were being abused.

He said the demonstrations had quickly led the country to "the brink" and that calling in the military had been necessary to restore stability and safety.

"Our economy came to the brink of collapse," Sheikh Khalid said. "So we had no choice but to protect the interests of our country ... from collapse, from total collapse internally. And from external threats."