BAGHDAD – Gunmen killed eight security guards and made off with nearly $7 million during a brazen bank robbery Tuesday in central Baghdad in the second such assault in a week. While overall violence is down in Iraq, ordinary crime has emerged as an increasing threat to the country's stability.

Police said the robberies appeared to be the work of militants seeking money for operations after their funding was severely curtailed in US-Iraqi military crackdowns.

An Iraqi soldier stands guard near a US armoured vehicle during a reopening ceremony of a bridge connecting Shula and Ghazaliya districts in Baghdad July 28, 2009. [Agencies]

The retaliatory sectarian violence that pushed Iraq to the brink of civil war has declined dramatically over the past two years. But armed robberies targeting jewelry stores, currency exchanges and pawn shops appear to be on the rise.

Interior Minister Jawad al-Bolani said he had ordered an investigations and called for increased security measures for banks.

"There should be some warning system within banks, and the bank safe should not be easily opened," he told The Associated Press. "These gangs have shifted from kidnapping into bank robberies to finance terrorist operations."

"This crime constitutes a challenge as the district is located in a well-protected area," government spokesman Ali al-Dabbagh said.

The gunmen broke into the state-run Rafidain Bank at about 4 am, killing three on-duty guards and five others on the premises who were either on a break or asleep, according to Iraqi police. They seized 8 billion Iraqi Dinars ($6.9 million), the Interior Ministry said.

It was not immediately known how many gunmen were involved or how the money was secured in the bank at the time of he robbery.

Iraqi and US officials blamed the attacks on militants trying to raise funds for operations, although they did not elaborate on the reason for that conclusion or which side they believed was responsible.