(CNN) -- Police in Bahrain regularly resort to beating anti-government protesters, despite officials' pledges to stop such practices, a human rights group said Sunday.
A Bahraini government spokesman denied that allegation and others made in the Human Rights Watch report.
"The allegations are absurd, and unfortunately, we ask for human rights organizations not to rely on unreliable sources," said government spokesman Abdul-Aziz bin Mubarak Al Khalifa.
Human Rights Watch said interviews revealed at least five instances in the past month in which police severely beat detainees -- some of whom were minors, according to a report issued after representatives from the group finished a five-day visit to the island nation.
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Visible injury marks appeared to confirm details of accounts from former detainees interviewed by Human Rights Watch, the organization said.
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Treatment of prisoners inside police stations and formal detention facilities has improved, Human Rights Watch said, and Bahrain appears to have made "rapid progress" in eliminating torture inside police stations after a committee last year recommended installing video cameras there.
But now, according to Human Rights Watch, beating and torture of prisoners is continuing at informal facilities and in secluded outdoor areas, where detainees have been taken for up to two hours before they're transferred to police stations.
"Bahrain's leaders need to make clear that they will investigate and punish those responsible for abuses when the cameras are off," Human Rights Watch said.
The Bahraini government spokesman said Human Rights Watch's relationship with political activists "is such that they don't check the legitimacy or facts behind the allegations."
CNN has not independently confirmed the rights group's report.
Al Khalifa said the government has taken steps to implement recommendations made by an independent commission last year. Dozens of officers are currently being investigated under a new government system to look into torture allegations, he said.
Sunday's Human Rights Watch report comes amid growing global scrutiny of the human rights situation in the Gulf state.
Earlier this month opposition groups in Bahrain and politicians around the world called for officials to cancel a Formula 1 race as violent clashes continued between activists and authorities. The Bahrain Grand Prix continued as scheduled, but protesters used the international spotlight on the race to call for the release of Abdulhadi al-Khawaja, a detained human rights activist who has been on a hunger strike for more than two months.
The activist, who was arrested last April for his role in anti-government demonstrations that swept through his country, is protesting his life prison sentence. Last June, al-Khawaja and seven other Shiite opposition activists were found guilty of plotting to overthrow the country's Sunni royal family.
On Sunday, Bahrain's information ministry denied that it was force-feeding al-Khawaja, saying in statement that al-Khawaja gave consent for doctors to insert a naso-gastric tube for nutrition after his blood sugar dropped.
Demonstrations in Bahrain failed to gain the traction of other Arab Spring uprisings after a crackdown by authorities in the island state, backed by troops from nearby Saudi Arabia and the United Arab Emirates.
In November of last year, Bahrain's Independent Commission of Inquiry issued a report critical of authorities' reactions to the protests, which began in February 2011, spurred by uprisings in Tunisia and Egypt.
The independent commission, set up by Bahrain's King Hamad bin Isa al-Khalifa, found that between February and April of last year, 35 people were killed in unrest there.
Two senior international advisers to Bahrain's chief of public security told Human Rights Watch they had visited some of the informal facilities identified by the group, but found no evidence of detainees being taken there and mistreated. The chief said the government planned to improve police training to stop abuse, according to Human Rights Watch.
Earlier this month, the state-run Bahrain News Agency published a statement responding to another report by Human Rights Watch that alleged Bahrain had not lived up to its commitments on reform.
The nation's Ministry of Human Rights and Social Development dismissed the criticism as rash, saying that Human Rights Watch report "had ignored the positive developments in the country and the continuation of the reform process," and that it was committed to the protection of human rights.
CNN's Elizabeth Joseph, Mohammed Jamjoom and Peter Wilkinson contributed to this report.