A bomb targeting Sunni mourners in Baghdad killed 15 people on Monday, the third in a series of attacks on funerals that have raised the spectre of all-out sectarian conflict.

The blast in Adhamiyah, a Sunni area of north Baghdad, wounded another 30 people, while violence elsewhere in the country killed seven more, officials said.

The latest attacks came amid a months-long spike in unrest that has raised concerns Iraq is slipping back into the rampant violence that peaked in 2006 and 2007 and left tens of thousands dead.

The Adhamiyah bombing came after a suicide bomber struck a Sunni funeral in Baghdad on Sunday, killing 12 people, and two blasts targeting Shiite mourners killed 73 on Saturday.

And on Friday, two bombs exploded in a Sunni mosque near Samarra, north of Baghdad, killing 18 others.

There are persistent fears, bolstered by a spate of sectarian attacks this year, of a return to widespread Sunni-Shiite sectarian conflict.

Prime Minister Nuri al-Maliki said in a statement released earlier on Monday that attacks in Iraq aimed to "reignite sectarian strife" and divide the country.

And the United Nations warned of the danger of revenge attacks after the Saturday blasts.

"Retaliation can only bring more violence and it is the responsibility of all leaders to take strong action not to let violence escalate further," said Gyorgy Busztin, the UN's deputy special representative for Iraq.

The US embassy issued a statement on Monday condemning recent attacks on mourners, saying that they "remind us of the formidable security challenges that Iraq faces."

More attacks struck northern Iraq on Monday.

A bomb exploded near an ambulance that was carrying a pregnant woman to a hospital near the city of Mosul, wounding her and the driver and killing one of her relatives and a medic.

The woman was in labour at the time of the blast. Her child, a boy, was delivered by Caesarian section and was in good health, a medical source said.

Nineveh province, of which Mosul is the capital, is one of the most dangerous areas of Iraq, with militants carrying out near-daily attacks.

Insurgents have a major presence in Mosul and are said to extort money from shop owners in the city.

Gunmen killed a tribal sheikh and three other people in Mosul on Monday, and a farmer near Baiji to its south was also shot dead.

Violence in Iraq has reached a level this year not seen since 2008, a surge in unrest that authorities have so far failed to stem.

With the latest violence, more than 610 people have been killed this month and over 4,400 since the beginning of the year, according to AFP figures based on security and medical sources.

In addition to major security problems, the government has also failed to provide adequate basic services such as electricity and clean water, and corruption is widespread.

And political squabbling has paralysed the government, which has passed almost no major legislation in years.