Three Americans were shot and killed by an Afghan security guard at a hospital in Kabul, Afghanistan on Thursday.

Officials say the three Americans killed were doctors, including a visiting father and son.

A fourth doctor as well as an American nurse were wounded in the shooting, USA TODAY reports.

District Police Chief Hafiz Khan said a guard at Cure International Hospital turned his weapon on the staff he was supposed to be guarding and began shooting.

"Five doctors had entered the compound of the hospital and were walking toward the building when the guard opened fire on them," said Kanishka Bektash Torkystani, a spokesman for the Ministry of Health. "Three foreign doctors were killed."

The identities of the victims were not released to the public. The U.S. Embassy in Kabul confirms that the victims were American but did not give more information.

A large number of Afghan national police remain in front of the Cure hospital, which is down the street from the former King's palace.

Pacha Mir, a 52-year-old taxi driver, said he was waiting in a taxi at the front of the hospital when he heard 15 gunshots at around 10:15 a.m. local time.

"I was really scared," he said. "Then we started to escape from the area."

Minister of Health Soraya Dalil said two of the victims were a visiting father and son, adding that another victim was a Cure International doctor who had worked in Kabul for seven years.

The attacker is alive and remains at a military hospital after being shot in the stomach by other police officers inside the hospital, according to Sediq Sediqi, a spokesman for the Ministry of the Interior.

"We will find out the motive because he's alive," Sediqi said.

The attack at the hospital, which specializes in maternity and child health, is the latest incident in a string of attacks on foreigners in Kabul.

In January, more than a dozen people were killed at a Kabul restaurant by suicide bombers and gunmen. Then in March, gunmen killed several diners at a restaurant at an upscale Kabul hotel.

Earlier in April, an Afghan police officer shot two Associated Press staff members who were working in Khost, killing photographer Anja Niedringhaus and wounding correspondent Kathy Gannon.

"It's about an act of one person," Sediqi said in reference to the hospital attack, saying it is not known if the attacker had terrorist connections.

The investigation into the shooting is ongoing.