KIRKUK, Iraq (AFP) - Militants who have overrun a swathe of territory north of Baghdad in a lightning offensive released on Thursday 48 foreigners, including four Turks, held for several days, Iraqi police said.

The construction workers, who were helping build a hospital in the now insurgent-held city of Tikrit, are from Turkey, Nepal, Bangladesh, Turkmenistan and Azerbaijan.

"The workers... were kidnapped near the Hamreen mountains four days ago, and were handed over near a checkpoint between Tikrit and Kirkuk," said Major General Torhan Abdulrahman, the deputy police chief for Kirkuk province. "We brought them to Kirkuk, and they will return to their countries soon."

Sunni militants have seized dozens of foreigners, including 40 Indians and more than 40 Turks, since launching last week a swift offensive and capturing a swathe of territory across four Iraqi provinces.

Security forces performed poorly when faced with the initial militant offensive, in some cases shedding uniforms to flee. They appear to have at least somewhat recovered from the shock of the onslaught, regaining ground in some areas, but militants have still managed to advance in others.