Chimpanzees are on the loose in a Swedish zoo after escaping their enclosure. Zookeepers have already shot 4 of them.

• A band of chimpanzees busted out of their enclosure at a Swedish zoo this week.
• The incident prompted staffers to shoot four of the primates, three fatally.

A band of chimpanzees busted out of their enclosure at a Swedish zoo this week and some are still on the loose inside the animal park, according to officials and reports.

Five of the seven chimpanzees at Sweden's Furuvik Zoo escaped from their enclosure on Wednesday and three of them were shot dead for "safety reasons," zoo officials said. Another one was reportedly shot and wounded.

In a series of statements posted to its website, the zoo said it had no choice but to take lethal action against the chimps and that decision to do so was "extremely painful for all of us."

The animal park said that chimpanzees can be perceived as "peaceful," but they are "extremely dangerous."

Chimps, the zoo said, "are fast, very strong and generally fearless" and added that a situation "can quickly escalate into a life-threatening" one.

The use of tranquilizers on the escaped primates was not an option, according to the zoo, which said that the method requires someone to be up close to the animal and takes minutes to go into effect.

If a chimpanzee is on the loose in the animal park, staffers "unfortunately have to shoot to kill," the zoo said.

The zoo said that it does not yet know how the chimps escaped from their enclosure and is launching a full investigation into the matter.

The zoo staffers have managed to feed the other loose chimps and are working to get them back in their enclosure, the zoo said in an update on Friday.

"Until these chimpanzees are secured in the enclosure, we are still on full alert and it is still an ongoing serious situation," the animal park said.

The zoo said that the chimps are "very loved" and acknowledged that the situation was "terrible."

"We understand that the sadness and upset is great for many people right now and we are incredibly sorry that this situation could arise," the animal park said, adding that it takes "full responsibility for this tragic situation."