The treatment of two elderly elephants at the Hanoi public zoo has drawn outrage in Vietnam, with animal rights groups demanding the pair be relocated.
The groups are calling for the two female elephants -- Thai and Banang -- to be released to a national park, and close to 70,000 people have signed an online petition in support.
Vietnamese state media have also covered the story widely in recent weeks.
On Wednesday morning, the pair's legs were in chains as zookeepers fed them grass and sugarcane, AFP journalists observed.
"The elephants are quite fierce. With a broken electric fence, we had to chain them," a zoo staff member told AFP on the condition of anonymity.
Staff said the two elephants were brought to the zoo from the country's south and central highlands in 2010 and 2014.
"They were not in the same herd. We had to do our best to help prevent fighting between them and ensure safety for carers," the zoo employee said, adding that the animals were well cared for and given three meals a day.
But Animals Asia sent a letter to city authorities earlier this month urging the creatures be returned to the jungle at the Yok Don National Park in the country's central highlands.
"Elephants at the Hanoi zoo have been chained for a very long period," the group said in the letter.
"The health of the two elephants will deteriorate if they remain as they are."
Vietnam Animal Eyes, a group of local animal advocates, started a petition to remove the pair from the zoo at the beginning of August.
Zoo director Le Si Dung, however, has characterized the push to free the animals as "illogical," according to state media.
"The two elephants, aged 60-70 years old, have been at our zoo for more than 10 years. ...They will die if they are put back to nature as they do not know how to seek food or protect themselves," Dung was quoted as saying by the Dan Tri news site.
David Neale, animal welfare director at Animals Asia, told AFP the elephants were likely frustrated by not being able to carry out their natural behaviors.
"Yok Don National Park ... has all of the elements which an elephant needs to be able to live well and live happily," he said.
Other animal lovers believe the zoo is not serving the elephants' best interests.
"This (Hanoi) zoo is like a jail," social media user Thanh Nguyen said. "I was furious after my first visit there last year... I would never go back."
According to environmental groups, Vietnam's wild elephant population has fallen from around 2,000 in 1980 to about 100 in 2022.
The number of domesticated elephants has also declined significantly from about 600 in 1980 to 165 today.