Baghdad (CNN) -- Three more U.S. service members were killed in Iraq, making June the deadliest month for American troops in combat since 2008.

A total of 14 troops have been killed in combat this month, and another service member died in a noncombat-related incident. This was the highest number of combat deaths since June 2008, when 23 U.S. service members were killed.

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Fatalities in Iraq have dropped dramatically in recent years for American troops. The latest deaths came Wednesday, just six months before all U.S. service members are scheduled to depart the country under a bilateral agreement forged between both nations.

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The service members died in a rocket attack near the Iranian border in southern Iraq. A U.S. official told CNN that the attack has every indication of being conducted by an Iranian-backed Shiite militia.

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An increase in attacks in recent months against American troops has been blamed on Shiite militias.

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Iraq is weighing whether to request that some of the 47,000 troops in Iraq stay beyond the January 1, 2012, deadline.

CNN's Jomana Karadsheh contributed to this report.