Prime Minister Narendra Modi on Friday expressed grief at the passing of Vietnamese President Tran Dai Quang, who passed away following a serious illness at the age of 61.

“Deepest and heartfelt condolences to the Party, nation and people of Vietnam, and to the family of Member of the Politburo and President of the Socialist Republic of Vietnam H.E. Mr. Trần Dai Quang,” the PM wrote on Twitter.

“We have fond memories of his great friendship for India and his successful state visit in March this year,” the PM said recalling the late President’s visit during which India and Vietnam agreed on increased cooperation in areas of defence especially maritime security.

We have fond memories of his great friendship for India and his successful state visit in March this year. pic.twitter.com/m6IHEuXPvb

— Narendra Modi (@narendramodi) September 21, 2018

According to the official Vietnam News Agency, Tran Dai Quang passed away from a “serious illness despite devoted treatment by professors and doctors” both in Vietnam and abroad.

Quang had been President since April 2016 and was known as a tough leader with little tolerance for dissent.

Before becoming the President, Quang served at the powerful Ministry of Public Security for more than four decades.

The position of President is ceremonial in Vietnam, where the real power lies with the Prime Minister and the Communist Party chief.

Quang’s last high-level diplomatic engagement was during Indonesian President Joko Widodo visit to Hanoi last week. At the time, Quang had appeared thin and pale in public and was unstable on his feet.

His last public appearance was just two days ago, at a meeting with visiting Chinese politicians and foreign dignitaries in Hanoi.

Quang’s visit to India came amid his country’s simmering conflict with Beijing over the South China Sea.

In the joint statement issued in New Delhi, Modi and Quang had expressed their commitment to ensure that respect for sovereignty and international law continues to be upheld. The commitment was an indirect reference to China’s aggressive posture in the South China Sea region, which has been criticised by Southeast Asian nations as well as world powers.

Read More: Vietnamese President Tran Dai Quang dies following prolonged illness

The Vietnamese President said that the two nations are striving to bring bilateral trade to $50 billion by 2020. He underlined his country’s commitment to creating favourable conditions for businesses in areas ranging from Information technology to Infrastructure.

But Quang’s rule was not without controversies. As president, he oversaw a crackdown on dissidents that rights groups have decried as a chokehold on free expression. More than 40 people were jailed this year and some 100 have been behind bars as of April 2018, according to Amnesty International.