Kabul, Afghanistan (CNN) -- Investigators were traveling to western Afghanistan on Thursday to probe a shootout that killed two Spanish soldiers, an interpreter and a police officer.
The international team left Kabul to perform "an initial assessment" of the shooting.
In the Wednesday incideent, shots were fired by an Afghan National Police officer during a mentoring session, killing the soldiers and the interpreter. The police officer was killed when an ISAF member returned fire.
The assessment team is made up of officials from the Afghan Interior and Defense Ministries and NATO's International Security Assistance Force.
It "will review evidence, gather facts and talk with people who can provide details of what happened," ISAF said in a news release.
ISAF said that "at this point, the cause of the shooting is unclear."
"These incidents are still very isolated. The coalition forces are training thousands of Afghan Army and Police Forces every day," said Brig. Gen. Josef Blotz, ISAF spokesperson. "Training the Afghan National Security Forces remains as the foundation of a successful Afghan-led transition strategy."
The shootout occurred at the Qala-i-Naw base in Badghis province, according to the Spanish Interior Ministry.
The Spaniards are training the Afghan police in a course that is intended to improve professional skills, according to ISAF's website.
Spanish Interior Minister Alfredo Perez Rubalcaba told reporters Wednesday that despite the tragedy, Spain will continue training Afghan forces.
CNN's Joe Sterling contributed to this report