The U.S.-led coalition in Afghanistan apologized on Friday for accidentally killing a 2-year-old boy in an airstrike. The crisis marks the latest obstacle to finalizing a security agreement between the U.S. and Afghanistan. 

On Thursday, President Hamid Karzai condemned the U.S. military for the death, and accused coalition troops serving in Afghanistan of "oppressions." The U.S. quickly issued damage control to try to minimize the anger from the strike, which also wounded two women, The Washington Post reports. 

Marine Gen. Joseph F. Dunford Jr., commander of U.S. and coalition forces in Afghanistan, called President Karzai to apologize to him personally. The coalition also issued a statement that it "deeply regrets" the incident. 

The incident further strains the United States' diplomatic ties with the country. President Karzai has been dismissive of plans to keep up to 100,000 U.S. soldiers in Afghanistan after 2014. Karzi said he may wait until next year to make a decision about the issue, but the U.S. is urging him to sign the agreement by the end of this year, according to NBC News. If he does not, the U.S. will make plans to withdraw all forces from Afghanistan by the end of 2014. 

A spokesman for Karzai said on Friday that the agreement will only be signed after there is an "absolute end to all military operations and airstrikes on residential areas by foreign troops which can result in civilian casualties."

The incident occurred when a U.S. drone fired into a house before noon on Thursday in the province of Helmand. A child was killed during an operation that was targeting "an insurgent riding a motorbike." A coalition official said that the child was on the road at the time of the explosion. 

The intended target, who was killed, was a "mid-level Taliban commander who had been involved in attacks" on coalition troops and was "organizing and facilitating lethal aid to insurgents in the area," said a coalition spokesman.

During the call to Karzai, Dunford promised to launch an investigation into the drone strike. 

The governor of Helmand and other local officials said that it was just one of two coalition strikes, and that a "farmer in a field" was also killed by a suspected U.S. drone on Thursday.