(CNN) -- Bahraini authorities opened an investigation Friday into the death of a teenage anti-government protester after a report by the medical examiner of the public prosecution blamed the death on injury caused by birdshot and a report from Bahrain International Hospital blamed the death on a drop in blood pressure that led to cardiac arrest.
Opposition groups al-Wefaq and the Bahrain Center for Human Rights say he was killed by security forces,
Citing the general director of northern governate police, the Ministry of Interior said Friday in a statement that the boy, identified as Ahmed Jaber Ali Al Qattan, was taken Thursday to Bahrain International Hospital, where efforts to resuscitate him failed.
An official with the Ministry of Interior "reiterated its commitment to implement greater transparency in law enforcement and noted that the Department of Legal Affairs was immediately assigned to investigate about the circumstances of Al Qattan's death," a news release from the government's Information Affairs Authority said.
The public prosecution ordered the body taken to Salmaniya Medical Complex Public, where the coroner's initial report blamed the death on an injury caused by birdshot, the release added.
The Department of Legal Affairs has been assigned to investigate the death and the outcome will be made public, the statement said.
Al-Wefaq, the country's largest opposition party, and the Bahrain Center for Human Rights said the teen was killed during a demonstration in the capital city of Manama. Both groups gave the boy's age as 16; the government put his age at 17.
On Friday, thousands of demonstrators evaded a roadblock set up by Bahraini security forces to attend al-Jaber's funeral, said Matar Matar, a former member of Parliament from the al-Wefaq Party, who said that he attended a portion of the funeral.
After the burial, mourners took to the streets to demand the downfall of the regime and chanted slogans against the al-Khalifa ruling family, Matar told CNN. When security forces responded with tear gas and rubber bullets, a few people in the crowd threw stones at the authorities, he added. Several people were injured during the clashes, but by night calm had been restored to the capital, he said. The Ministry of Information says security forces interfered to disperse more than 20 individuals involved in blocking nearby roads.
"There was a great sense of outrage today," Matar said. "The government claims they will investigate the death and that an independent commission of monitors has been formed, but the injuries and deaths continue to happen. Woman and children must be careful."
CNN cannot independently confirm Matar's account; the Bahraini government could not be reached for comment to respond to the allegations.
Protests have occurred in Bahrain for months despite a crackdown by the kingdom's Sunni monarchy, backed by troops from Saudi Arabia and the United Arab Emirates. The al-Khalifa family is Sunni Muslim; two-thirds of the country's people are Shiite.
More than 30 people have been killed during the demonstrations, which began in February and during which activists say Bahraini security forces used live ammunition against protesters.
Opposition groups say more than 1,000 people -- mainly Shiites -- have been detained and more than 2,000 have lost their jobs for allegedly taking part in the protests.
The incident comes on the heels of a government announcement that it will give a new trial to a group of 20 medical staff convicted of trying to overthrow the government.
Bahrain's Information Affairs Authority said the public prosecutor announced the new trial for the medical staff, who received prison sentences ranging from five to 15 years.
The 20 were detained during protests. Their conviction last week sparked anger among human rights groups and the international community. The U.S. State Department said it was "deeply disturbed." Amnesty International called it a "travesty of justice."
"The retrial will be conducted before the highest civil court in Bahrain," Attorney General Ali Al-Boainain said Wednesday in the government's statement.
"The Department of Public Prosecution seeks to establish the truth and to enforce the law, while protecting the rights of the accused. By virtue of the retrials, the accused will have the benefit of full re-evaluation of evidence and full opportunity to present their defenses."
However, doubts have been raised by some of those involved over how different the new trial would be.
Two medics who spoke Thursday to CNN via Skype said that a statement issued by the government in Arabic differed from the English version -- and that the Arabic version would apply to their case.
Fatima Haji said the medics' lawyers were trying to clarify what the government intended.
Haji said she feared the new trial could follow the same procedure as the military court trial that resulted in their conviction.
She suggested the government was trying to manipulate the international media by trying to give a different picture of events.
Dentist Nada Dhaif said the government had sought to attack them in the media, and that the military court had not listened to evidence or witnesses in their defense.
If they had been given a fair trial in the military court, then all the medics would have been found innocent, she said.
According to a translation of the Arabic statement, the attorney general said the prosecution wants to "ensure that the law is correctly applied."
The attorney general "stressed that the charges do not include convicting a person because of his or her humanitarian duty or political opinion, since the law does not permit that," the translation states.
In Wednesday's announcement, the Bahraini government rejected the suggestion that the medical staff were being charged simply for doing their jobs.
"Contrary to allegations that the medics were tried for treating patients, the charges included possession of unlicensed weapons; taking over specific sections of Salmaniya Medical Complex; participating in illegal protests on hospital grounds; refusing to treat certain patients; misuse and theft of hospital property and supplies; propagating false news, and inciting sectarian hatred," the statement said.
CNN's Mohammed Jamjoom contributed to this report.