An international medical aid group that once won the Nobel Peace Prize is pulling out of Iraq, citing the recent targeting of aid workers by militant groups.

Médecins Sans Frontières, also known as Doctors Without Borders, said on Thursday that it has decided with "a great degree of regret and sadness" to shut down its three aid centres in Baghdad and to cancel plans to open a fourth in Fallujah.

"It has become impossible for MSF as an organization to guarantee an acceptable level of security for our staff, be they foreign or Iraqi ," said Gorik Ooms, the general director of the Belgium-based group.

The three medical aid centres in Baghdad, being run by about 90 Iraqi nationals in the mainly Shia Muslim neighbourhood of Sadr City, had seen more than 100,000 patients since January.

Last month, CARE International ended its operations in Iraq after militants kidnapped its director in the country, Margaret Hassan. Her captors have threatened to kill her unless Britain pulls its troops out of Iraq.