A suicide bomber attacked the main checkpoint to Baghdad International Airport on Wednesday, wounding at least 15 Iraqis, the military said.

The explosion shortly after 9 a.m. destroyed several vehicles, sent up a huge cloud of black smoke, and was followed by militants firing machine guns at security forces. It also underscored the difficulties U.S. and Iraqi authorities face in curbing the rampant insurgency.

In New York, Iraqi Foreign Minister Hoshyar Zebari said U.S.-led forces must remain in Iraq until the country's own soldiers and police can take responsibility for securing the nation amid its continuing insurgency.

U.S. soldiers captured four wanted militants in a number of separate raids since Monday, including a former spy in Saddam Hussein's secret service believed to be financing several terrorist groups in western Baghdad's Ghazaliyah district, the military said.

Click here for full story