A US tourist realized a robbery wasn't a joke when a masked robber put a gun to her head and a military veteran in her tour group grabbed the young assailant and killed him with his bare hands.

"I thought it was a skit. But then he pointed the gun at my head and grabbed me by the throat and I thought I was going to die," Clova Adams, 54, told The Associated Press by telephone from the Carnival Liberty cruise ship on Friday, two days after the thwarted robbery.

The assault took place during a ship stopover in Limon, 130 kilometers (80 miles) east of San Jose, Costa Rica's capital.

Adams was part of a group of 12 American tourists who hired a local driver to explore Costa Rica foSr a few hours. They were climbing out of the van to a visit a Caribbean beach when three masked men ran toward them. One held a gun to her head, while the other two pulled out knives.

Suddenly, one of the tourists, a US military veteran estimated to be in his 70s, jumped out of the van and put the gunman in a headlock, according Limon police chief Luis Hernandez.

Hernandez said the man, whom he refused to identify, struggled with the robber, breaking his clavicle and eventually killing him. Police identified the dead assailant as Warner Segura, 20. The other two robbers fled.

The US Embassy confirmed the account, and also refused to release the name of the US tourist who defended the group, citing his right to privacy.

Sergio Lopez, a Red Cross auxiliary, examined Segura's body and said he died from asphyxiation.

Lopez also treated Adams for a panic attack.

"She was very nervous after the assault, but she had not she had not been physically hurt," Lopez said.

Costa Rican officials interviewed the group, but said they wouldn't charge the US tourist with any crime because he acted in self defense.

"They were in their right to defend themselves after being held up," Hernandez said.

He said Segura had previous charges against him for assault.

The cruise ship delayed its departure until the group was released and again boarded the ship, The Carnival Liberty, which was set to return Sunday to Fort Lauderdale, Florida.

Adams spoke with the AP until a man who identified himself as her fiancee said they didn't want to talk to the press. He said the group might release a joint statement later, without elaborating. Adams did not say what state or city she came from.

Costa Rica has struggled with growing violence and crime in recent years. University of Kansas student Shannon Martin, 23, was stabbed to death in 2001 after she left a nightclub in Golfito, 105 miles (170 kilometers) south of San Jose.

Carnival Cruise Lines confirmed in a statement that one of the ship's guests had killed the Costa Rican assailant, but refused to name those involved.

"All of the guests involved, who had booked the cruise together as a group, have opted to continue with their vacation plans. Carnival is providing full support and assistance to the guests," the statement said.