GAUHATI, India (AP) — More than 100 animals, including 10 one-horn rhinoceroses, have died due to massive flooding at the famed Kaziranga game reserve in northeastern India, prompting Britain's Prince William and his wife, Kate Middleton, to express their concern in a letter to park authorities, officials said Saturday.

“Since the first week of June, we are having no respite with wave after wave of flood that has wreaked havoc inside the Kaziranga National Park and Tiger Reserve," said Kaziranga's park director, P. Sivakumar.

He said an animal that drowned in a swollen river near the park on Saturday brought the rhinoceros death toll up to 10.

The Duke and Duchess of Cambridge wrote to Sivakumar expressing their distress about the devastation to Kaziranga National Park and its precious wildlife. The couple had visited the park in April 2016 to learn about conservation and anti-poaching efforts.

“The deaths of so many animals, including one-horned rhino, are deeply upsetting,” they wrote.

The ongoing monsoon has dumped rain across parts of India, Bangladesh and Nepal, displacing 9.6 million people, according to the International Federation of Red Cross and Red Crescent Societies, or IFRC.

More than 550 people have been killed in the floods, the IFRC said.

The organization warned of a humanitarian crisis, saying that close to one third of Bangladesh has already been flooded, with more flooding expected in the coming weeks. It said that 2.8 million people have been affected, and that more than 1 million are isolated.

In India, over 6.8 million people have been affected by the flooding, mainly in the northern states of Assam, West Bengal, Bihar and Meghalaya bordering Bangladesh, the IFRC said, citing official figures.

In Bihar, at least 10 people have been killed, the state's disaster management authority said Saturday.

Though officials have opened relief centers in affected districts, people have instead chosen to shelter in tarpaulin tents set up along highways and embankments.

The Bihar government has requested help from India's air force to airdrop relief materials including food packets, the disaster management authority said.

In Assam, home to Kaziranga, 96 people have been killed in floods and another 26 have been killed in mudslides. Some 50,000 people have sought shelter in government-run relief camps.

The floodwaters are making protecting wildlife within the park more difficult, too.

“More than a hundred of the 223 security camps inside the sprawling park are still submerged, making day-to-day work of our 1,600 guards really challenging,” Sivakumar said.

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Singh reported from Patna, India.