A Jordanian police officer killed two Americans, a South African, and a fellow Jordanian at a police training facility outside the capital Amman on Monday before being fatally shot by local forces.
Jordanian and American officials say the gunman also wounded six others, including Americans and Jordanians.
The U.S. government has used the Jordan International Police Training Center in Muwaqqer, about 30 kilometers from Amman, in cooperation with Jordan, to train tens of thousands of police cadets from the Middle East since the site opened in 2003.
A senior U.S. official confirms the Americans killed were part of the State Department police training program.
A Jordanian government spokesman says an investigation is underway to determine the "motives behind the crime."
Local and international media identified the shooter as 28-year-old police Captain Anwar Abu Zeid.
At the White House, President Barack Obama said the U.S. is taking the attack "very seriously" and that the United States will be working closely with Jordanian authorities "to determine what exactly happened."
U.S. Central Command tells VOA that all American military personnel in Jordan are accounted for. The deceased worked as contractors with Jordan's Public Security Department, Jordanian government spokesman Mohammad Momani said in a statement released by Petra news agency.
The U.S. and Jordanian governments signed an agreement in 2003 establishing the facility. Using a multi-national group of experts alongside Jordanian staff, the center began training classes of would-be police officers from neighboring Iraq. The effort later included training Palestinian security forces.
The shooting coincides with the 10 year anniversary of one of the worst attacks in the kingdom's history, when suicide bombers at three hotels in Amman killed more than 50 people on Nov. 9, 2005.
Three bombers died in the blasts. Earlier this year, Jordan executed Sajida al-Rishawi, who was convicted for her part as a failed suicide attacker. Al-Qaida in Iraq claimed responsibility for the bombings.
In 2002, USAID official Laurence Foley was shot to death outside his home in Amman. Abu Musab al-Zarqawi, who later became commander of al-Qaida in Iraq, was sentenced to death in absentia for ordering the killing. Two other men were executed in 2006 for carrying out the assassination, and a third was sentenced to death.
Zarqawi, a Jordanian, was killed in a U.S. airstrike in Iraq in June 2006.
VOA National Security Correspondent Jeff Seldin and State Department Correspondent Pam Dockins contributed to this report.