Iraqi teenagers widely perceived to be gay are being brutally killed in Baghdad with Shiite militias distributing lists of targets warning of further assaults, officials and human rights groups say.

At least 15 teenagers, described as "emos" for their tight-fitting black clothes and alternative hairstyles, have been stoned, beaten to death or shot dead in the past month, medics say.

Reports have also said some of them had their heads smashed with concrete blocks.

Human rights groups say the death toll is far higher amid accusations of a cover-up by security forces.

Witnesses in the conservative Shiite Muslim bastion of Sadr City in north Baghdad say a militia group calling itself the "Brigades of Anger" has posted leaflets naming 22 youths to be "punished".

Medical officials said at least 15 have already been killed in the past month, including seven who were stoned to death, five who were shot and one who was beaten to death. At least two of the victims were girls.

"Police generally take care of all these incidents," said one of the officials, who declined to be named. "They don't like medics or ambulances to take them. Two days ago, the body of a teenager was found in Bayaa -- he was evacuated by police."

In Western youth culture, the term emo refers only to appearance and musical preference and carries no connotation about a person's sexual orientation.

In Iraq, however, the term is widely conflated with being gay, which remains taboo in the conservative Muslim country.

The International Gay and Lesbian Human Rights Commission, based in New York, said a "new surge of anti-gay violence" since February in Iraq had seen nearly 40 people kidnapped, tortured and murdered.

"There are no excuses for such heinous human rights violations," said Cary Alan Johnson, the organisation's executive director.

"We demand that the Iraqi government put a stop to the wanton persecution and killing of gay people, and that the perpetrators be punished."

Iraq's interior ministry said in a March 8 statement that it had not recorded any anti-gay or anti-emo killings. It said the recent murders in the capital had been for "revenge, or social, criminal, political or cultural reasons."

In a February 13 statement that remains on its website, however, it described emos as "devil-worshippers" and added that the ministry "has official approval to eliminate them as soon as possible."

In the statement, police Colonel Mustaq Talib Mohammedawi, described as chief of Baghdad's "social police", said his forces would enter the capital's schools as part of its efforts to target the "phenomenon".

The violence has drawn criticism from religious leaders, with Shiite cleric Mohammed al-Yaqoubi arguing that any response to emo teenagers should be confined to "advice, guidance and knowledge."

Iraqi human rights ministry spokesman Kamil al-Amin added that any government response should not extend beyond "education."

Human Rights Watch warned in August 2009 of Iraqi militias torturing and executing men they suspected of homosexuality, and accused authorities of turning a blind eye to the violence.

The New-York based group said hundreds of men were kidnapped, tortured and killed that year in a wave of violence that began in the Sadr City stronghold of radical Shiite cleric Moqtada al-Sadr.

London-based Amnesty International wrote a letter to Iraqi Prime Minister Nuri al-Maliki in April 2009 urging government protection for homosexuals.

Homosexuality is forbidden in Islam, frowned upon in Arab society and illegal in many Middle Eastern countries. Iraq has no law against homosexuality but prominent religious authorities have harshly condemned it.