By Brendan O'Brien

(Reuters) - Three Christian missionaries from Missions in Haiti were shot and killed in an ambush by a gang in Haiti, the Oklahoma-based group said on Friday.

The missionaries were taking shelter in a house when gang members began shooting at the residence at about 9 p.m. CDT (0200 GMT) Thursday, the group said in two Facebook (NASDAQ:) posts.

Months of gang violence in Haiti have forced the government into retreat, and U.S. Secretary of State Antony Blinken has warned the country is close to becoming a failed state.

Haiti’s main international airport in Port-au-Prince reopened this week, nearly three months after it shut due to deadly gang-related violence. But gangs still control much of the capital and Haiti's main seaport remains closed.

"Unfortunately, this serves as a reminder that the security situation in Haiti cannot wait – too many innocent lives are being lost," State Department spokesman Matthew Miller said in a statement.

Missouri State Representative Ben Baker said his daughter Natalie Lloyd and son-in-law Davy Lloyd were killed while working as full-time missionaries. Davy Lloyd was the son of the organization's founders, David and Alicia Lloyd, who started it in 2000.

The identity of the third person killed has not been released.

"My heart is broken in a thousand pieces. I’ve never felt this kind of pain," Baker said on Facebook.

Missions in Haiti said the couple was leaving a church when they were ambushed by three trucks full of gang members. They took Davy Lloyd to a house, tied him up and beat him, before taking the group's trucks and some items and left, it said.

"Another gang came after to see what was going on and if they could help, so they say," the organization said. "No one understood what they were doing, not sure what took place but one was shot and killed and now this gang went into full attack mode."

The couple and another individual identified as Jude called a leader of the organization on a satellite phone and said that their lives were in danger.