KABUL, Afghanistan - Three Americans - a pediatrician and a father and son - were killed by an Afghan government security officer at a hospital Thursday, the latest in a series of attacks on foreign civilians that have rattled aid workers, contractors, and journalists.

Another American, a female medical worker, was wounded in the attack at Cure International Hospital of Kabul, run by a Pennsylvania-based Christian charity, officials said. The gunman also was wounded.

The hospital staff performed surgery on the attacker, who had shot himself, before he was handed over to Afghan authorities, Cure said in a statement. An Afghan government spokesman said the assailant was shot by other security guards.

The attacker's motive was not clear, police said, and the Taliban denied responsibility.

Among the dead was Jerry Umanos, a 57-year-old pediatrician from Chicago, according to his mother-in-law, Angie Schuitema. The Lawndale Christian Health Center in Chicago said Umanos worked there for more than 16 years before moving to Afghanistan in 2005.

The other two slain Americans were a father and son, who were visiting the hospital, said hospital and Afghan officials. Victims' names and hometowns had not been released by Thursday night.

The shooting continued a deadly pattern of attacks on civilian targets.

In January, a Taliban attack on a popular restaurant in Kabul killed more than a dozen. On April 4, an Afghan police officer shot two Associated Press journalists working in the eastern province of Khost, killing photographer Anja Niedringhaus and wounding reporter Kathy Gannon.

The hospital shooting is also the second "insider attack" this month by a member of Afghan security forces targeting foreign civilians.

While aid groups have been targeted before, the frequency of such attacks has disturbed a community used to the daily risk of working in conflict zones.

"We're not seeing aid workers running for the airport, but many organizations are taking a careful look at their security postures," said Graeme Smith, an analyst in Kabul for the International Crisis Group. "The hard reality is that the country is becoming more violent, and Kabul has not escaped this pattern."

Mark Knecht, Cure International's chief financial officer, told reporters outside the group's headquarters in Lemoyne, in Cumberland County, that it "remains committed to serve the people of Afghanistan."

Violence has spiked overall in Afghanistan as insurgents sought to disrupt the April 5 presidential election and sow insecurity ahead of the troop pullout, nearly 13 years after the U.S.-led invasion to topple the Taliban's radical Islamic regime.

Afghan civilians have suffered the longest. A U.N. report said 2,959 Afghan civilians were killed last year, up 7 percent.

Among U.S. service personnel, at least 2,177 Americans have died since 2001 serving in Afghanistan.

Foreign workers who once moved relatively freely - if carefully - in the capital are taking even more precautions.

After so many years of an international presence, many Afghans appear to have shifted views on foreigners in general from celebrating them as liberators to resenting them as de facto occupiers whose money is drying up now that the international mission is winding down.

The Cure hospital, along a busy highway, is regarded as more modern and sanitary than most in Afghanistan. Patients sometimes travel hours by bus to get treatment there. It is guarded by a few private security personnel in addition to Afghan police stationed at nearby checkpoints.

Complicating the picture in the hospital shooting is that it was an "insider attack" by a member of Afghan security forces.

The hospital attacker, who has not been identified, served in the Afghan Public Protection Force and was assigned as a guard at the facility, District Police Chief Hafiz Khan said. The APPF is an armed security force under the Interior Ministry that was created to protect foreign organizations.

The gunman entered the hospital through a visitors entrance and fired on Umanos and two American visitors he was greeting, Afghan security officials said. The pair, a father and son, were not part of the hospital's staff, said Dr. Yousof Khan, the hospital's deputy director.

Lately, Umanos is said to have grown worried about his safety in Kabul, telling a friend in the United States that he had been shot at while jogging.

"He was obviously concerned," said the friend, Art Jones. "At the same time, you can't count the number of children that Jerry's impacted, the lives he's saved on his own and with the doctors he trained. That's who he was. He was driven by the kids."

In Chicago, at the Umanos family home, his wife, Jan Schuitema, said: "Our families and friends have suffered a great loss, and our hearts are aching. We don't hold any ill will toward Afghanistan in general or even the gunman who did this. We don't know what his history is."

INSIDE

Despite the tragedy, Cure International won't abandon its mission. A8.

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This article contains information from the Los Angeles Times.