BAGHDAD — The American military announced on Thursday that three more American soldiers had been killed this week, as the combat-related deaths for United States forces in Iraq reached a monthly toll not seen since 2008.

The deaths occurred Wednesday in southern Iraq, and the military did not disclose details on how the soldiers died. A military spokesman confirmed that they were killed by enemy attack. Recently, the increase in casualties has been attributed to rocket or mortar attacks on American bases by Shiite militias. American convoys have also come under increasing threat from improvised explosive devices.