(AP) -- Two more Americans have been identified as killed in the attacks on Brussels, the State Department confirmed Sunday, bringing to four the total number of U.S. citizens confirmed as victims.

The State Department said, "We express our deepest condolences" to those who lost loved ones in the attack, but declined to identify them publicly.

Officials have said previously that at least a dozen Americans were injured in the attack last Tuesday.

Earlier Sunday, the White House said that President Barack Obama telephoned the parents of an American couple identified as among the dead in last week's attacks.

The White House said Obama offered his condolences and praised Justin and Stephanie Shults as epitomizing all that was good about America.

Justin Shults was originally from Gatlinburg, Tennessee, and his wife, Stephanie, was a native of Lexington, Kentucky. They graduated together from Vanderbilt University's Owen Graduate School of Management. A family member says they were dropping Stephanie's mother off at the airport and were watching her walk through security when the bombs went off.

The White House said the president also assured their parents that the thoughts, prayers and resolve of the nation are with them at this difficult time.

Thirty-one people were killed and 270 injured in the attacks Tuesday at the Brussels airport and a train station.