The Japanese zoo housing Punch, a macaque that went viral for clinging to an orangutan plushie after being abandoned by its mother, said on Tuesday it was considering a full ban on photography near the monkey enclosure following an incident involving two US citizens.

The incident on 17 May involved two Americans entering the monkey enclosure at the Ichikawa City Zoo in Chiba prefecture without permission.

The zoo responded by widening the buffer zone around the enclosure and installing anti-intrusion netting.

Police on Tuesday referred the two Americans to prosecutors on suspicion of forcible obstruction of business.

Reid Jahnai Dayson, 24, claimed to be a university student while the second suspect, Neal Jabahri Duan, 27, identified himself as a singer.

According to investigators, the Americans conspired to trespass into the enclosure at around 10.50am. While the younger man climbed over a fence and jumped into the enclosure dressed in a character costume, the other filmed the stunt on a smartphone from outside and later shared the footage on social media.

Neither person got close to the animals before they were detained by staff.

Nearly 60 monkeys, including Punch, were inside the enclosure at the time.

The zoo later said they had discussed “future responses with the Ichikawa City” which “included a full ban on filming at Saruyama”.

“Regarding the methods for a full ban and the impacts that it would have, we will proceed with further deliberations. Additionally, we have received numerous inquiries and proposals regarding filming from YouTubers and others, but in light of this situation, we’ll hold them in abeyance for the time being,” the zoo said.

Starting 19 May, the zoo said it was expanding the viewing restriction area, installing nets to prevent intrusion and starting constant patrols. “We apologise for any further inconvenience and ask for your understanding.”

Takashi Yasunaga, head of the Ichikawa government’s zoological and botanical garden division, said the intrusion put both animals and zoo staff at risk.

“We want to take various measures to ensure something like this never happens again,” he was quoted as saying by AFP.

Punch went viral earlier this year after the baby macaque was filmed cuddling an orangutan plush toy that zookeepers had supplied after he was rejected by other monkeys.

The clips drew huge crowds to the zoo, forcing officials to introduce rules asking visitors to stay quiet and limit viewing time to 10 minutes to avoid stressing Punch and the other monkeys.

Punch’s popularity sparked a surge in visitors to the Ichikawa City Zoo, outside Tokyo.