The United States has expressed regret over the killing of 16 Afghan civilians by a U.S. soldier stationed in Afghanistan and is trying to deal with the situation.

The White House said in a statement that President Barack Obama telephoned Afghan President Hamid Karzai on Sunday to express his “shock and sadness” over the reported killing.

The White House said that Obama, describing the incident as “tragic and shocking," extended his condolences to the people of Afghanistan, making clear his administration’s commitment to establish the facts as quickly as possible and to hold anyone responsible fully accountable.

Defense Secretary Leon Panetta also called Karzai to express his condolences and pledged to bring those responsible to justice.

U.S. lawmakers are also urging the administration to take measures to prevent the incident from aggravating.

On Sunday morning, a U.S. soldier walked out of his military base in Kandahar province and opened fire, killing 16 civilians, including women and children.