Iraqi security forces found about 100 badly decomposed bodies in a mass grave north of Baghdad, the US military said on Saturday, one of the largest such finds in the country for months.

US and Iraqi security forces said it was not clear who was responsible for the grave near Khalis, 80 kilometres north of Baghdad, or when the victims had been killed.

'Initial reports indicate it may contain the remains of approximately 100 people,' said US military spokesman Major Winfield Danielson.

Iraqi police said they suspected those in the grave were likely to have been killed some time after the 2003 US-led invasion to topple Saddam Hussein. Tens of thousands of Iraqis have been killed in sectarian fighting between majority Shi'ites and minority Sunni Arabs and in a mainly Sunni Arab insurgency since the invasion.

'The skeletal remains appear to have been in the grave for a long time, and we have not yet determined who might be responsible for their death and burial,' Danielson said. 

Mass graves are found fairly regularly in Iraq but the latest one near Khalis is among the largest in recent months. US and Iraqi forces often blame Sunni Islamist Al Qaeda for the mass killings and graves.

Last month a grave with about 50 bodies was found near Samarra, 100 km north of Baghdad, during a hunt for Al Qaeda fighters. Mass graves dating back to Saddam's rule have also been found, although these have tended to be in desert areas of southern Iraq.

In 2003, Iraqi and US human rights investigators said they suspected Iraq had up to 260 mass graves containing the bodies of up to 300,000 people murdered during Saddam's rule.  Many of the victims were thought to be Kurds, against whom Saddam waged military campaigns in the 1980s and '90s, and Shi'ites who staged an uprising in 1991.-Reuters