Thailand has expressed condolences to Cambodia over the loss of Deputy Prime Minister Sok An, a right-hand man of Prime Minister Hun Sen.
Foreign Minister Don Pramudwinai said on Thursday the government will send representatives to attend his funeral.
Sok An, a close aide to the Cambodian prime minister for more than two decades, died on Wednesday. He was 66.
Sok An had served as deputy prime minister since 2004 and died in a Beijing hospital, where he had received medical treatment over the previous few days.
He suffered from a kidney illness and had spent some months in a hospital in Singapore prior to his transfer to the hospital in the Chinese capital.
Hun Sen flew to Beijing on Monday, according to his aide.
Sok An had been a minister of the Office of the Council of Ministers since 1992, prior to which he served as secretary general of the Foreign Ministry, Cambodia's ambassador to India and deputy foreign minister, in that order.
As a minister, his duties ranged from overseeing the airline industry and archaeological projects at the ancient temples of Angkor, to serving as chief negotiator with the United Nations on establishment of a Khmer Rouge tribunal.
Local media said that Sok An ran the government like "a Hindu god of 48 arms".
"This is a loss of the most active human resource who sacrificed everything for the sake of the Cambodian people," Cambodian government spokesman Phay Siphan said, adding that the cause of death had yet to be confirmed.
Sok An's deteriorating health prompted Cambodia on Monday to abruptly cancel a visit to Cambodia by Deputy Prime Minister Somkid Jatusripitak scheduled for Tuesday for trade and investment talks.