Gunmen shot dead at least seven women and five men at a Baghdad brothel, in the same area where alcohol shops were hit by a deadly attack last week, officials said.

Iraq is struggling to contain a wave of violence that, with the latest unrest, has killed more than 400 people in May -- the second month in a row in which attacks have cost over 400 lives.

The murders took place at a large red and white two-storey house with a backyard surrounded by a sheet metal fence, in a quiet residential part of the capital's eastern Zayouna district.

Area residents said they neither heard nor saw anything out of the ordinary, and an interior ministry official said the unidentified gunmen used silenced weapons.

Soldiers and police mainly armed with Kalashnikov assault rifles and pistols cordoned off the site, which was visited by high-ranking officers.

Journalists were not permitted to enter the house, or to take photographs or video.

On May 14, gunmen restrained police at a checkpoint in the area, then shot dead 12 people at a row of adjoining alcohol shops nearby.

Both prostitution and alcohol are prohibited by Islam, the religion of the vast majority of Iraq's population.

Zayouna is an upscale, mixed district of Sunni and Shiite Muslims where brothels have proliferated in recent years.

In other violence on Wednesday, a roadside bomb exploded in a market near Baquba, north of Baghdad, killing two people and wounding a third, a police lieutenant colonel and a doctor said.

Police also killed six militants in the northern city of Mosul, officials said.

And security forces killed two members of the Ansar al-Sunna militant group and wounded a third in the city of Kirkuk, also in the north, police Major General Torhan Abdulrahman said.

Prime Minister Nuri al-Maliki has announced a shakeup of top security officers in the country, and defence ministry spokesman Mohammed al-Askari told Al-Hurra TV on Wednesday that 14 commanders have been changed so far.

But the security problems in Iraq go far beyond who is commanding the country's forces.

Tensions are festering between the government of Maliki, a Shiite, and Sunnis who accuse authorities of marginalising and targeting their community, including through wrongful detentions and accusations of involvement in terrorism.

Protests broke out in Sunni areas of Iraq almost five months ago.

While the government has made some concessions aimed at placating the protesters and Iraqi Sunnis in general, such as freeing prisoners and raising the salaries of Sunni anti-Al-Qaeda fighters, underlying issues have yet to be addressed.