(CNN) -- Bahrain police on Friday denied opposition claims that security forces were responsible for the death of an anti-government protester, saying the man died from natural causes.
The death of 19-year-old Mohammed Ibrahim Yacoub was one of four reported Thursday by the Bahrain Center for Human Rights.
The opposition group al Wefaq accused Bahraini authorities of running over Yacoub with a police car, an allegation the Ministry of Health denied, according to the Bahrain News Agency (BNA).
As part of its denial, the Health Ministry released a video purportedly taken at the time of the arrest that it alleges shows Yacoub unharmed. It also released a medical report that indicated Yacoub died from "sickle cell complications" and that his body was "free of injuries."
Bahraini police said Yacoub was arrested Wednesday for participating in "acts of violence and vandalism," BNA reported. Police also said he died of natural causes, the news agency said.
The reports of deaths come just weeks before demonstrators are expected to mark the one year anniversary of protests demanding political reform and greater freedoms in Sunni-ruled, Shiite-majority Bahrain.
The State Department issued a travel advisory this week for U.S. citizens, warning of potential unrest in Bahrain.
"Spontaneous and sometimes violent anti-government demonstrations occur in some neighborhoods, particularly at night and on weekends," the warning said.
"The demonstrations have included blockades of major highways, trash can fires and establishment of unofficial checkpoints. Participants have thrown Molotov cocktails and used various other homemade weapons."
Bahraini authorities, according to the statement, have responded with the routine use of tear gas, stun guns and other crowd control measures.
While the State Department said there is no indication that U.S. citizens are being targeted, it said its Embassy personnel and their family members were being relocated to other neighborhoods that have not been involved in the protests.
Protests began February 14, 2011, in Bahrain -- spurred by uprisings in Tunisia and Egypt.
But the protests failed to gain the traction of other Arab Spring uprisings following a crackdown in February and then again in mid-March by Bahraini authorities -- backed by troops from Saudi Arabia and the United Arab Emirates.
Demonstrators and Bahraini authorities have continued to clash, with the opposition accusing the government of being heavy handed in its crackdown on protests.
In November, Bahrain's Independent Commission of Inquiry issued a report highly critical of the crackdown.
The commission, set up by the king, concluded that police had used excessive force and torture during last year's crackdown on protests. Abuse of detainees included beatings with metal pipes and batons, and threats of rape and electrocution, commission Chairman Mahmoud Cherif Bassiouni said at the time.
The mistreatment included physical and psychological torture, intended to extract information or to punish those held by security forces, he said.
The report recommended reforms to the country's law and better training of its security forces.
CNN's Mohammed Jamjoom and Salma Abdelaziz contributed to this report