President A P J Abdul Kalam, Prime Minister Manmohan Singh [Images] and Congress president Sonia Gandhi [Images] and ministers were among those who paid tributes to National Security Advisor J N Dixit who died of a massive heart attack in New Delhi [Images] on Monday morning.

The President placed a wreath on the body at Dixit's residence.

• J N Dixit no more

Singh expressed shock at the death. "I have lost a close friend, a valued colleague and a great source of support and advice," he said in a condolence message to Mrs Dixit. "The nation has lost a true patriot, a great diplomat and a wise strategist," he added.

Defence Minister Pranab Mukherjee said, "We are deeply shocked at the sudden demise of the national security adviser." "He was quite hale and hearty on Saturday when we met and discussed national security issues," Mukherjee said.

Union Home Minister Shivraj Patil [Images], External Affairs Minister K Natwar Singh, Delhi Governor B L Joshi and Chief Minister Sheila Dikshit, Iranian Ambassador in India Yajazoubi and Air Chief S P Tyagi also paid tributes to Dixit.

Natwar Singh said Dixit was his colleague and friend for 45 years and an outstanding member of the Indian Foreign Service. It would be difficult to fill the void created by his death, he added.

• J N Dixit: An astute diplomat and strategist

Former prime minister Atal Bihari Vajpayee and Bharatiya Janata Party president and Leader of Opposition Lal Kishenchand Advani [Images] also paid tributes to Dixit.

Principal Scientific Adviser to the Government of India Dr R Chidambaram also expressed 'deep shock' at Dixit's demise.

"We were trying to do a lot of things together in the national security area, and the news of the demise has made me terribly sad," Chidambaram told PTI on phone.

"India has lost a great diplomat and a guide," he added.

Atomic Energy Commission Chairman and Secretary, Department of Atomic Energy, Dr Anil Kakodkar said Dixit's death is a 'big loss to the country'.

"Dixit had been a strong support to our nuclear programmes. He was very knowledgeable and knew all the nuances of foreign affairs," Kakodkar told PTI.

Diplomats also paid glowing tributes to their former colleague.

"Not only was he at the right place at the right time, he was also the right man for the right job," former Indian high commissioner to Pakistan G Parthasarathy said condoling the death.

The national security adviser's post today, when India is a nuclear power, has a key role to play not only with regard to foreign policy but also to keep nuclear deterrent in order. "'Mani' (Dixit), who was like many of us, for long felt that India needed a nuclear deterrent," Parthasarathy said.

He recalled that when he was Indian ambassador to Myanmar and Dixit was the foreign secretary, India was thinking of changing its policies to seek the support of Myanmar to fight insurgency in the North East.

"When I fought a lone battle, 'Mani' Dixit was the one person who backed me," he said.

Former foreign secretary Muchkund Dubey said the death was a 'very big loss' to the Foreign Service and to the government.

"He was playing a key role. I think he was a towering personality as far as the conduct of our foreign policy was concerned," Dubey said.

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US Ambassador Robert Mulford also expressed grief at the death. "Throughout his distinguished career, Dixit played a central role in improving the US-India relationship, most notably as foreign secretary in the early 1990s and recently as National Security Adviser," a US Embassy release said.

"Dixit leaves behind many American friends and admirers," it said.