The stabbing of two Christians at a retreat centre in Maryland has left workers "heartbroken", a board member said.

Peter Chang of the Anna Prayer Mountain Church Retreat Center in Urbana told the Associated Press that the incident should prompt workers to be wary of welcoming those with suspected mental health issues. However, he also noted "that's what we're here for".

The stabbing, which took place on July 26, resulted in the death of 62-year-old Chung Hwan Park. His wife, Ae Suk Ko, 57, was also injured in the attack. The couple were missionaries from South Korea, and worked as cooks at the centre. Police said that Park was stabbed a total of 13 times, and Ko, four.

A 30-year-old homeless man, identified as Song Su Kim, has been charged with first-degree murder, first-degree attempted murder and two counts of assault. He is said to have been living at the centre for five days before the incident.

Of Korean decent, Kim told police that he had been treated badly by all Koreans and wanted to "invade a Korean" in retaliation, according to charging documents. He is now being held without bail.

Reports suggest that Kim first attacked Park with a kitchen knife and then stabbed Ko when she tried to defend her husband.