KABUL, Afghanistan — An Afghan security guard opened fire on a group of foreign doctors at a Kabul hospital today, killing three American physicians and wounding a U.S. nurse, officials said.

The shooting at Cure International Hospital in western Kabul was the latest in a string of deadly attacks on foreign civilians in the Afghan capital.

Two of the dead Americans were a father and son, Minister of Health Soraya Dalil said, adding the third American was a Cure International doctor who had worked for seven years in Kabul.

Dalil said an American nurse also was wounded in the attack.

“A child specialist doctor who was working in this hospital for the last seven years for the people of Afghanistan was killed and also two others who were here to meet him, and they were also American nationals, were killed,” Dalil said. “The two visitors were father and son, and a woman who was also in the visiting group was wounded.”

The attacker was a member of the Afghan Public Protection Force assigned to guard the hospital, according to District Police Chief Hafiz Khan. He said the man’s motive was not yet clear.

The gunman was wounded and in custody. He was in surgery at midday in the same medical facility under heavy police guard, according to Kanishka Bektash Torkystani, a Ministry of Health spokesman.

It was unclear how the attacker was wounded.

The U.S. Embassy in Kabul confirmed that three American citizens had been killed in the hospital attack but said it had no other information.

According to its website, the Cure International Hospital was founded in 2005 by invitation of the Afghan Ministry of Health. It sees 37,000 patients a year, specializing in child and maternity health as well as general surgery. It is affiliated with the Christian charity Cure International.